Can a T-Mobile phone work with a different SIM Card?

[Shee]

I found this great phone online, but it's a T-Mobile, and it includes a mobile plan.
I want to use it with a different SIM card (not a T-Mobile card).
Will it work? I heard about needing to unlock it.
How do we do that? Is it guaranteed to work outside the US?
Thanks!

 

[vamsii]

After unlocking your can use any sim card in your mobile.This can be done through codes.
This unlocking code will be provided by your network provider.
Or you may get it from online providers like Wickedunlock.com .They will help you to unlock your mobile easily.