I have a new unlocked GSM phone. I want to take it to Egypt with me in a month for my vacation. If I have it activated now with a Cingular or T-Mobile pre-paid "Go Phone" type of plan where you just pay ahead for a certain number of minutes, will they "lock" the phone so that it just works on their GSM band, or will the phone remain unlocked so that all I have to do is change the SIM card to an Egyptian one when I get to Egypt? I just want to know if I will have to un-lock the phone before I go. Any help is appreciated. Thanks!