I will be cutting the Verizon cord come Dec 3rd, and porting my long beloved number to Google Voice; I've been using Groove IP & Google Voice for the past week with my Nexus 4 and before that on the GNex. Calls from Groove are spotty, download speeds are always faster than upload, so you will always hear callers better than they can hear you. Calls on HSPA will work ok to poor on most places; I do find myself shouting and repeating a lot, so for those instances, using the 100 minutes will come in handy.
I do get decent WiFi at home and work; home works better with calls; in & out; but for some reason I only ping less than 1megs up at work, so calls are ok, but really poor for the most part. So, I bought in-hear microphone & earphones and am taking & making calls on gmail. When I get into work, I exit my Groove App, and calls into my Google Voice gets forwarded to Gmail... pretty sweet...
Between the 100 minutes in 'emergencies', gmail & my land-line; most people shouldn't know the difference. I'll try for another few weeks, but I might try Straight Talk with unlimited minutes just to ease the hassle, but I will still keep my number on Google Voice...