...roaming is turned on in your account? Is it possible you use to have a post-paid plan (w/o any roaming) and now have a gophone plan? See here:
http://www.att.com/shop/wireless/plans/prepaidplans.html#tabInternational
Unfortunately there's no data roaming, but if you are on wifi you could indeed use something like whatsapp (Bob's suggestion).
If there's something else amiss here, visit howardforums.com to see if anyone in the pre-paid or Gophone sub-forum can answer your question.
ATT's user forums have gotten a lot better too. Link:
http://forums.att.com/t5/AT-T-Wireless-Community/ct-p/attwireless
I have an AT&T Gophone (Nokia Lumia 520) and I'm currently living in Mexico. I'm on a pay-as-you-go plan. As some of you may know, when you fly from the U.S. (where the carrier shows on the phone as AT&T) to Mexico, the carrier shown on the phone switches to Telcel. I can call/text U.S. numbers from here without any problems. Where I'm struggling is with texting/SMS to local Mexico numbers, especially Mexico cell numbers. I've tried virtually every combination of country codes, area codes, +'s, and I keep getting "error-invalid number" messages when I try to text. In my phone messaging settings, the SMS center number is the standard AT&T number....312 314 9810. Could that be part of the problem? Any help/suggestions appreciated.....
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