The Windows Phone 7 is on T-Mobile. I have been carrying around both phones. In my experience, Verizon has been far superior in getting the phone to work.
However, this was not meant to be a post about that. I want to just focus on my new Verizon phone... the iPhone 4.
In short, the phone is excellent. Having worked with previous iPhones, everything is as it should be... except, I can make calls on it consistently. When I carried around an AT&T iPhone as a demo, it was great and fun to play with, except that I couldn't count on it when I really needed to, to be a phone.
I also pay for the tethering package from Verizon. This allows me to use the phone as a 3G modem if I am in a hotel and they want me to pay $15 for internet access per day. Tethering is integrated nicely into the iPhone.
In short... the Verizon iPhone is an iPhone that also works as a phone consistently.