Can you use T-Mobile with an iPhone 4?

I already have a plan with T-Mobile and I love it, so I really don't want to switch to AT&T, but I love the iPhone too! Can I have the T-Mobile service plan with the iPhone 4?

HI yes you can use your t-mobile sim in iphone 4 only if it is unlocked one ..Else if your iphone 4 is locked with some other network provider then until you unlock it you can't use it with t-mobile sim ..You can easily unlock your iphone 4 from network lock with the help of providers like Simpleunlocking.com here they will unlock your iphone 4 using remote unlocking service for affordable cost ...