My iPhone 4 is not allowing me to send text messages?

I'm able to send and receive txt messages perfectly within USA I have AT&T as my wireless carrier. Once I cross the border to mexico II am able to receive messages but I can't reply because it won't send the message. The first time I went down to Mexico I was able to send some messages but then after some messages it stopped sending messages. This last time I went it never allowed me to send messages but I was able to receive messages. How can I send messages what can I do

I also have At&t and a iPhone 4, I have crossed to Mexico before also. This happens also sometimes due to the network settings you have maybe not have roaming on. You can find that in your settings to turn it on, if the problem persist you may call AT&T and tell them your in Mexico but live in the USA and maybe they can change some network settings and get it working again

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