Cell Phone?

I have this cell phone Sony Ericsoon for Cingular. I wanted to change Sim card, so, I took one from my t- mobile cellphone. When I insert it, it sais insert right smart card. How to fix itCell Phone?
this message comes up because you've inserted a sim card from a different carrier. if the phone is from cingular then you can only use cingular sim cards but if you want to use your t-mobile sim card on it then i suggest bringing the phone to any cell phone vender(i suggest t-mobile since you're using their sim card) and ask for them to unlock the phone for you...this would cost you about 20-30 dollars.Cell Phone?
Your mobile is locked to a network. Go to the carier from weherever you got the phone and ask them to unlock them and be sure to bring a lot of money.Cell Phone?
All US carriers have registered their phones for their SIMS only, you can use other SIM only if you get ur phone unlocked, contact any software expert and he will help you outCell Phone?
Tmobile runs on a GSM band so it will not work with cell phones that are of Sprint, AT%26amp;T and Cingular wireless. The best thing for you to do is to find out a local store that unlocks cell phones and have them do it, it might cost between $25-40 dollars or less. If you are not able to do that then, just sell the phone on ebay as a sony ericsson cell phone which is locked on a cingular network, if you know for sure it works for cingular, as tested.