what WON'T work on an unlocked iPhone?

well, I may keep my t-mobile service just until it's death.. and was wondering. If I DO pick up an iPhone and unlock it through FREESIM. I know that visual voice mail won't work, but what other features won't work? What happens if I add applications such as the few AIM programs that are available?

Basically all I'm asking is, could we get a list of what will and what won't work with an unlocked iPhone?

Thanks