Two weeks ago in Mexico I purchased a Telcel mini sim and put it in my Sprint Iphone 4s. It worked perfectly. For $2 per day (prepaid) I got all my imessage, emails and forwarded skype calls. I was so happy saving on roaming charges. Last week I inserted the Telcel sim again. Now all I get is ATT. If I manual select carrier-Telcel, I get 1 unusable bar, then ATT. I tried it again yesterday, same thing. I kept driving away from the border (ATT tower), about 40 miles in and an hour later I finally got Telcel, maybe because there was no AT&T signal around. My phone worked perfectly all the way back to the US with Telcel and did not pick up ATT again. This is very frustrating. I put the Telecel sim into my wifes iphone4s and same thing happened. I have not upgraded software or changed anything, why wont the I4s detect Telcel in Telcel territory. Could an update have been pushed to my phone or something? Help?