I have an unlocked T-Mobile BlackBerry Peal 8120 in a Pre-Paid Plan with T-Mobile (only voice services). I travel by land from Texas to Mexico occasionally for business. To avoid international roaming charges, at the time I cross the US-Mexico border I change the SIM card in the BlackBerry and use a local pre-paid SIM card from the Mexico Operator Telcel. I turn off the phone in the border area to avoid picking up roaming signals from the other side of the border. I turn on the phone until I'm far from the border area (at least 60 miles away from the border). I make sure that the phone displays the local Operator in the BlackBerry display.
I started noticing that every time I returned to the US (I put back the T-Mobile SIM Card when I cross the US border) my balance was reduced significantly. I called T-Mobile Customer Service and they told me that I had several roaming calls during my days in Mexico. In my last trip, my T-Mobile balance was reduced from $40 to $0 in roaming calls. How can this be possible? T-Mobile Customer Service did not believe that I switched the SIM card while in Mexico and said they will not refund the roaming charges. Is the BlackBerry storing information from the old SIM Card when I switch to the local SIM card in Mexico? Is the BlackBerry using WiFi (UMA) to connect to the T-Mobile network to charge roaming? Again, how can be possible to be charged for roaming if I do not have the T-Mobile card inserted?
