If you mean SMS messgaes (text) you probably need to enter the SMS message center number.
Existing and New AT&T customers The message center number for all existing and new AT&T SIM cards is
+13123149810. If experiencing problems with
text messaging, please
contact Customer Care.
Former AT&T Wireless customers The message center number for all former AT&T Wireless customers is
+19703769301.
Former Cellular One from Dobson customers The message center number for all former Cellular One from Dobson customers is
+13305310005.
×