Someone just pointed out this feature I didn't know existed in Windows Mobile. When you have a contact highlighted you can press the d-pad Left and Right keys to change communication methods for the person (work, home, mobile, txt, email etc). Watch really close when pressing Left/Right, and you'll see the tiny "w" turn to "m", "h", "e" etc.
I suppose this is most useful for alternating default phone numbers - when you press Talk, the selected number is dialed. Previously I used to just open the contact and select the number I wanted to call from the card view. My coworker thinks this is much faster. Agree?