I have been using GV (it was called grandcentral before Google bought it) since 2006 and I had never had problems. It was not able to call out at that time and google added it after it changed to GV. I am using it on my asterisk 1.8 pbx and it has been very stable. The sound quality is great too. If you look at the international calling rate, you will figure out the GV is very cheap already. What I am trying to say is that it won't be very expensive even google decide to charge for it. Plus, you still have till the end of this year free.
