Should I get an iPhone 3G?

It's been two years and my contract with T-Mobile is up and I'm thinking of the iPhone 3G. I used to have a Windows Mobile (Pocket PC Cell Phone) from T-Mobile and have always had such devices. Everyone at work loves the iPhone and my boss has one too. Is there anything that should stop me from getting one? I do run Windows Vista and love it, but can't wait to see what Microsoft will do for windows mobile in the future. Thanks for your thoughts and opinions!