Can I unlock my iphone that is not paid off to switch to another carrier?

I've been wanting to get away from T-Mobile for awhile now but my iPhone isn't paid off. I read online that you can unlock your phone through one of those unlocking websites but I want to know if it will actually work since again my phone isn't paid off.

IPhones are hard to unlock and unlocking services don't guarantee unlocking, so you could lose money if it doesn't work. It's all a risk.

Search online to see if others have had luck unlocking their iPhone's through these services.