@addison
Yes I use a VOIP line instead of a "physical" phone.

You can use Gizmo5 (client running on tablet or using Nokia client or FRING or another VOIP client that can run on the tablet) or SIPgate or etc.

Why Google won't handle the whole process, IDK.

I think it's because their primary use-case is business people that have various home and work lines and need one line to manage them all.

If you use Google Voice call-out it will show the Google Voice # as the caller-id.

As far as being charged, well that depends. If you call via VOIP (tablet or any computer) then you cannot incur charges (just be sure you don't link your credit card with Google). However if you dial out via a home phone (call your GV #, during voicemail dial your PIN and then dial 2 and the number you want to call) then it will charge you for the call TO google (the entire call) so be sure that the GV # you pick isn't long-distance as far as your phone company is concerned. You are tunneling through the GV #. Now if you used a cellphone then it would use anytime minutes.

There are a bunch of guides out there. Search the forums, but the most popular is hornartist's. I also wrote one (not too popular though).