So I am working near the Mexico boarder and my iPhone 4S randomly picked up Mexico's cell phone towers. The AT&T symbol changed to Telecom and I had an "o" where it usually says 3G. My question is, why did my phone do this? I thought the phone had to be unlocked to use internationally. The scary thing is that I had to call AT&T to have them disable the data roaming feature from my account not knowing that my phone would do this automatically. I hope my next bill is not hundreds of dollars.