If your app pulls the user's phone number, make sure you check if that number is null or not. There seems to be a great number of user's who are using old SIM cards and the Android OS has a problem pulling the phone number so it's just blank (user's can check this by going to Settings -> About phone -> Status and looking at the phone number field). If everything's working you should see your phone number in there, but like I said there are quite a few who's fields are blank. Anyways, to fix this issue the user will need to call into T-Mobile's PDA Support department and have them do a MSSDN update over the air. This will reassociate the phone number with the SIM card and will cure this issue. Either that or swap out to a newer SIM, but the OTA update is faster. Just a little heads up for my fellow developers out there.