call the carrier and ask, if the new phone was not working, that is because you have to send the new IMEI number when you change phones. lots of people just stick the sim card in and think that is all they have to do, you have to call the carrier, and let them know you have changed phones so they can put the phone into the system. GSM phones communicate with the towers, and if your account has a nokia phone listed, and your using a Motorola with the old sim card, the towers will start to reject the signal since it is programed to find a nokia phone