Does T-Mobile support unlocked iPhone 4s?

My carrier is T-Mobile. I'd really like to purchase an iPhone 4S, though. I've even considered terminating my contract with T-Mobile due to their stubbornness to carry iPhones in their product lines (which I think is detrimental to their market share).

My question is, does T-Mobile USA support unlocked iPhone 4S phones? If I bought an iPhone 4S, would I be able to text, call, and browse the internet on it like I could with, say, Verizon, AT&T, or Sprint?

I'd also like to know, if I can use an unlocked iPhone 4S with T-Mobile, would I be able to use my unlimited data plan/wireless hotspot plan (under T-Mobile) on my iPhone 4S?

What are the setbacks of unlocking an iPhone with T-Mobile?

Any answers are appreciated.

Its not stubborness, they can't afford to carry the iphone.
you can use an iphone on tmobile but you will only get edge 2g, no 3g, 4g.

The other answer is false, you can definitely get 3G speeds with the iPhone 4 or 4S on T-Mobile. They are starting to re-frame towers in order to achieve this.