If you're looking for cheap VOIP services, check out voip.ms or callcentric.com. With a cheap SIP adapter (here's one $40 example), you can set up line(s) that range from free to $3 - $4 per month and will probably have all the features you need for a landline. You can certainly forward GV to any of them, if you don't want to port out the GV number, and inbound calls wouldn't ever know. For outbound calls that you want to show the GV number, you'd have to dial via the google voice app, or do the clunky dial GV first then dial out from another landline.