Which iPhone Carrier should I buy to unlock it?

[xGabriel]

I have t-mobile and definitely wouldn't change a carrier. On their site they allow unlocking iPhones and switching to T-Mobile. I did research and found it that it isn't really illegal.. So finally I can get the phone I always wanted

I don't know how to unlock but there is a store around me that does it for a price. I don't mind paying but which carrier should I buy it from and does it make a difference?
I am talking about the iPhone 4G.

Thank you very much.

(if this is the wrong section I apologize.)

 

[eastercat]

There is no iPhone 4G. Try again.

 

[Applejuiced]

If you're talking about Tmobile USA you will have to buy an unlocked iphone in order to work cause all US iphones are locked to AT&T.
Research a little more before you purchase cause not all iphones can be unlocked and there's different ways some better than the others.