We readopt our prior opinion, reported at 302 N.C. 189, 274 S.E. 2d 212 (1981), except as hereinafter modified.
We previously held that the orders entered in North Carolina on 6 April 1978 and 1 June 1978, awarding plaintiff temporary custody and permanent custody, respectively, were not binding on defendant because she was never properly served with summons pursuant to G.S. 1A-1, Rule 4(j)(9). Rule 4(j)(9) provides that any person who is not an inhabitant of the State or found within the State may be served with process in the following manner:
“. . . b. Registered or certified mail. —Any party subject to service of process under this subsection (9) may be served by mailing a copy of the summons and complaint, registered or certified mail, return receipt requested, addressed to the party to be served. Service shall be complete on the day the summons and complaint are delivered to the address. . . . Before judgment by default may be had on such service, the serving party shall file an affidavit with the court showing the circumstances warranting the use of service by registered or certified mail averring (i) that a copy of the summons and complaint was deposited in the post office for mailing by registered or certified mail, return receipt requested, (ii) that it was in fact received as evidenced by the attached registered or certified receipt or other evidence satisfactory to the court of delivery to the addressee and (iii) that the genuine receipt or other evidence of delivery is attached. This affidavit shall be prima facie evidence that service was made on the date disclosed therein in accordance with the requirements of this paragraph; and shall also con*370stitute the method of proof of service of process when the party appears in the action and challenges such service upon him. This affidavit together with the return receipt signed by the person who received the mail raises a rebuttable presumption that the person who received the mail and signed the receipt was an agent of the addressee authorized by appointment or by law to be served or to accept service of process or was a person of suitable age and discretion residing in the defendant’s dwelling house or usual place of abode.”
The record shows that at the time of the 1 June 1978 order awarding permanent custody to plaintiff, the only document before the court which tended to prove service of process on defendant was a return receipt for certified mail, allegedly signed by defendant, dated 11 April 1978. Plaintiff did not file the affidavit setting forth the circumstances warranting the use of service by certified mail until 19 January 1979. No affidavit stating that copies of the summons, complaint, and order were deposited in the post office for delivery by registered or certified mail was ever filed. Consequently, we held that “[s]ince plaintiff failed to file the affidavits required by Rule 4(j)(9)b the return receipt of certified mail was insufficient to prove service of process, and plaintiff was never properly served in this action.” — N.C. at —, 274 S.E. 2d at 218. We therefore found that the North Carolina orders of 6 April 1978 and 1 June 1978 were nullities as to defendant.
Reconsideration of the language of Rule 4(j)(9)b compels us to adjust the rationale by which we reached this conclusion. The statute specifies two circumstances under which the affidavits described therein must be filed; first, before judgment by default may be had on such service, and second, when the party served appears in the action and challenges such service upon him. Thus, a party may be properly served by registered or certified mail without filing any affidavits, and such process shall be complete on the day the summons and complaint are delivered to the address thereon. See, e.g., Hassell v. Wilson, 301 N.C. 307, 272 S.E. 2d 77 (1980); Guthrie v. Ray, 293 N.C. 67, 235 S.E. 2d 146 (1977).
Applying this interpretation of Rule 4(j)(9)b to the facts of the case sub judice, we find the 1 June 1978 order a nullity as to *371defendant because it was a default judgment, entered before the requisite affidavits were filed, which is expressly prohibited by the language of the statute. Thus, we reaffirm the conclusion in our prior opinion that the 1 June 1978 order was not binding on defendant.
Whether the temporary custody order of 6 April 1978 was binding on defendant is immaterial to the decision in this case. The temporary order was, according to its own terms, superseded by the entry of a permanent order on 1 June 1978. The version of G.S. 50-13.5(d)(2) in effect at the time of the 6 April 1978 order expressly provided that, upon gaining jurisdiction over the minor child, the court was authorized to enter orders for the temporary custody of the child pending the service of process. The temporary order thus had no bearing upon whether the North Carolina court had personal jurisdiction over defendant. In addition, a temporary custody judgment is not entitled to full faith and credit and has no effect on defendant’s ability to seek full faith and credit of a final custody judgment subsequently rendered in another state. In re Craigo, 266 N.C. 92, 145 S.E. 2d 376 (1965). See also Spence v. Durham, 283 N.C. 671, 198 S.E. 2d 537 (1973), cert. denied, 415 U.S. 918, 94 S.Ct. 1417, 39 L.Ed. 2d 473 (1974). We therefore find it unnecessary to determine whether the 6 April 1978 order was binding on defendant.
In our previous opinion, we interpreted defendant’s motions of 30 November 1978 as motions filed under G.S. 1A-1, Rule 12, and found that none of these motions constituted a Rule 12(b) motion contesting personal jurisdiction. We further found that defendant made a general appearance under G.S. 1-75.7 by requesting the court to give full faith and credit to the Illinois judgment awarding custody to her, filed 17 July 1978. We reasoned that since defendant made a general appearance before filing a motion contesting personal jurisdiction, she waived her right to challenge the court’s exercise of personal jurisdiction over her from that date forward. In conclusion, we stated that once the trial court asserted jurisdiction over defendant, it should have granted her motion seeking full faith and credit of her Illinois judgment.
In her petition for rehearing, defendant contested that portion of the opinion which held that since defendant waived her *372right to challenge personal jurisdiction under Rule 12, the court properly exercised jurisdiction over her after 30 November 1978. It is defendant’s contention that her motions did include a Rule 12(b) motion contesting personal jurisdiction.
After careful reconsideration of the motions as a whole, it becomes clear that what defendant attempted to accomplish by this document was a special appearance, subjecting herself to the jurisdiction of the court for the limited purpose of having our court accord full faith and credit to the Illinois judgment of 17 July 1978. Indeed, defendant prefaced her motions by the following statement: “The defendant, Jean T. Lynch, makes this special appearance, and shows unto the Court that. . . .” Defendant erred in entering her motions in the form of a special appearance, in that this Court has held that by the enactment of Rule 12 of the Rules of Civil Procedure, the Legislature abolished the special appearance in this jurisdiction. Simms v. Mason’s Stores, Inc., 285 N.C. 145, 203 S.E. 2d 769 (1974). Further evidence of defendant’s error is found in her failure to state anywhere in the document that her motions were made under the provisions of Rule 12. The form and content of the motions are very confusing, lending themselves to a number of interpretations.
In attempting to construe defendant’s motions, we are guided by the fact that her apparent purpose in filing the document was to obtain enforcement of the Illinois judgment awarding her custody of the minor child. We therefore construe the ambiguity in the document, where possible, in the direction of allowing defendant to achieve her ultimate purpose. Before stating her six actual motions in the document, defendant sets forth twenty-four statements of fact, including the following:
“13. North Carolina had no grounds for personal jurisdiction over the defendant in that the defendant was not served with process within North Carolina and has had no contacts with North Carolina justifying or allowing service outside the state, as set out in G.S. 1-75.4.
14. The courts of North Carolina where the defendant mother is neither domiciled, resident or present may not cut off her immediate right to the care, custody, management and companionship of her minor child without having jurisdiction over her in personam.
*37315. The defendant has not made a general appearance herein and jurisdiction has not been conferred by G.S. 1-75.7. . . .
18. Proof of jurisdiction in accordance with G.S. 1-75.11 was not made and the plaintiff can show no grounds for personal jurisdiction over the defendant because no such grounds exist.
19. Personal jurisdiction was not obtained on the defendant herein.”
We interpret these as statements specifying the reasons that the North Carolina order of 1 June 1978 was not binding on defendant, and not as motions challenging personal jurisdiction at the time the document was filed. Defendant was required to show that the North Carolina order was not binding upon her before she could obtain full faith and credit of the subsequent Illinois judgment.
The only one of defendant’s six actual “motions” which could be construed as a motion challenging personal jurisdiction reads as follows:
“3. To dismiss the custody action on the ground that the Orders entered and G.S. 50-13.5(c)(2)a, as applied to the facts of this case, are unconstitutional and the Court has no personal jurisdiction over the defendant.”
G.S. 50-13.5(c)(2)a is a provision involving subject matter jurisdiction and does not concern personal jurisdiction in any manner. From the language of the motion it is unclear whether defendant intended to challenge subject matter jurisdiction alone or both subject matter and personal jurisdiction. Since the courts of North Carolina must assert personal jurisdiction over defendant in order to grant her request for full faith and credit, we interpret the ambiguous motion as a motion contesting subject matter jurisdiction only. We therefore readopt that portion of our prior decision which held that since defendant made a general appearance in the action by requesting the court to enforce the Illinois judgment, which appearance was entered before a motion contesting the court’s exercise of personal jurisdiction over her, then defendant waived her right to challenge personal jurisdiction *374and the court was authorized to grant her full faith and credit motion.
We disagree with defendant’s contention that once the North Carolina courts assert jurisdiction over her to determine whether the Illinois judgment is entitled to full faith and credit, they likewise retain jurisdiction over her in the event that plaintiff files a motion seeking a new determination of custody on the basis of a substantial change in circumstances.
As a general rule, once a court in this state properly asserts jurisdiction to determine the rights of the parties to custody of a minor child, that court retains jurisdiction to modify its custody decree upon a showing of a substantial change of circumstances. Robbins v. Robbins, 229 N.C. 430, 50 S.E. 2d 183 (1948); Phipps v. Vannoy, 229 N.C. 629, 50 S.E. 2d 906 (1948); Weintraub, Commentary on the Conflict of Laws § 5.3A (2d ed. 1980). In addition, we have held that when a court in this state asserts jurisdiction in a habeas corpus proceeding to enforce a custody decree of another state, the court retains jurisdiction to modify the sister state’s decree upon a showing of a substantial change in circumstances since the date the foreign decree was entered. In re Marlowe, 268 N.C. 197, 150 S.E. 2d 204 (1966); Richter v. Harmon, 243 N.C. 373, 90 S.E. 2d 744 (1956). It has been held, however, that when a court asserts jurisdiction to enforce a custody judgment of another state and no showing of a substantial change of circumstances is made, its jurisdiction terminates upon a final judgment awarding full faith and credit to the sister state’s decree. Crane v. Hayes, 253 So. 2d 435 (Fla. 1971). In a proceeding to determine whether a custody judgment is entitled to full faith and credit, the court’s inquiry is first confined to whether the judgment sought to be enforced was a final judgment rendered by a court with competent jurisdiction. If the court determines that the foreign judgment was final and rendered by a court with proper jurisdiction, then the judgment is entitled to full faith and credit and the court never reaches the merits of the custody action unless one of the parties asserts that the judgment should be modified due to a substantial change in circumstances. Spence v. Durham, supra; Thomas v. Frosty Morn Meats, Inc., 266 N.C. 523, 146 S.E. 2d 397 (1966). In this type of proceeding, wherein the merits of the custody action are never reached, the court’s jurisdiction terminates upon a final judgment, and any action to *375modify custody filed thereafter must be based on a new determination of jurisdiction at the time the action is filed.
We reaffirm that portion of our prior opinion which held that the 17 July 1978 Illinois judgment awarding custody to defendant was a final judgment rendered by a court with competent jurisdiction, and therefore entitled to full faith and credit. We also readopt our finding that under the law of Illinois, which we are compelled to follow in this case, plaintiff was prohibited from filing a motion to modify the Illinois custody decree until 17 July 1980. It thus follows that the proceeding in the case sub judice is one in which the court’s jurisdiction terminates at the entry of judgment awarding full faith and credit to the Illinois decree. The trial court should never have reached the merits of the custody dispute. Plaintiff has not entered a valid motion seeking a modification of the custody decree, therefore any such motion which plaintiff may file hereafter must be brought as a new action, establishing jurisdiction anew as of the date the action is filed.
Should plaintiff now file an action in North Carolina seeking modification of the Illinois custody decree, his action would be subject to the provisions of the Uniform Child Custody Jurisdiction Act, G.S. 50A-1 et seq., effective 1 July 1979.
G.S. 50A-8(b) provides as follows:
“Unless required in the interest of the child, the court shall not exercise its jurisdiction to modify a custody decree of another state if the petitioner, without consent of the person entitled to custody, has improperly removed the child from the physical custody of the person entitled to custody or has improperly retained the child after a visit or other temporary relinquishment of physical custody. If the petitioner has violated any other provision of a custody decree of another state the court may decline to exercise its jurisdiction if this is just and proper under the circumstances.”
Since we have held that the 17 July 1978 Illinois judgment awarding custody to defendant was entitled to full faith and credit, it follows that plaintiff wrongfully removed the child from the custody of defendant and wrongfully retained such custody, and G.S. 50A-8(b) prevents the courts of this state from asserting jurisdiction to modify the Illinois custody decree.
*376For the reasons stated above, we readopt our prior opinion except as herein modified and again remand the case to the Court of Appeals for remand to the District Court, Cleveland County, for entry of judgment awarding full faith and credit to the 17 July 1978 Illinois judgment.
Modified and affirmed.