If you order new service with T-mobile you will receive a new sim. If oyu wish to keep your same number then you can port the number or to T-Mobile but then you will still receive a new Sim Card. Sim's are sensitive to the company you are with and only work with the company that you are with. But once you set up your sim, you then will keep all your information no matter what phone you go with, but it must be transfered to a phone within the same network.
I poked around for a while trying to find the answer for this, but didn't see it.
I currently have a Cingular phone. my contract ended last November, and I want a better phone, so I'm considering switching to T-mobile. i'm planning on buying everything online (phone/new plan). Do I need to buy a new SIM card or will one come with the new phone? Can I use my old Cingular sim card or is it pretty much dead to me now? i'd appreciate any help on this--i'm kind of confused about sim card locking and unlocking and whether it would be t-mobile to call to unlock my new phone or cingular to unlock my sim card. (i probably have it all wrong..) thanks.