I am slowly making my way to using Google Voice full time. It remains a bit of a hassle to make calls from my iPhone but the upside of using GV far out weighs the downside.
The biggest use I have for it is being able to initiate calls from my iMac or MacBook Pro and then, as soon as I finish the call, I can make notes or set a followup task for myself. I hated having to go to the GV website each time, however, so I went in search of a desktop widget that would serve the same function. I found it, and it is fantastic.
Voice Mac is a small application that is currently in Beta. It quietly sits in the corner of your screen waiting for you to make a call or send an SMS.
Want to call someone? Simply start typing their number or spelling their name. As you do the list is filtered until you can grab the person and the number you want. From there you can select which of your numbers you want to ring. Click either the phone or the SMS balloon and your call or SMS is initiated.
It is simple, it is fast and it it currently free. Grab it here.