I purchased an IP450 to use with my phone service from ,y cable company but they don't support that, then went to vontage but that did not work. I understand that I can use it with Google Voice but I'm not sure how to do that. Has anyone used a Voip phone with Google Voice?
If you're looking to have your phone work with your Google Voice service I've personally had success with FreePBX and the Google Voice/Chan Motif addon. Although we do not provide support for FreePBX or it's addons, in my experience, it's a pretty simplistic version of Asterisk that works quite well for this task.
In the past I've used AsteriskNOW 3.0.0 (a version of FreePBX running on CentOS) and installed it into a Virtual Machine using Oracle VM VirtualBox. Once installed you will need to create a SIP extension to register your phone to - the phone should register right up without issue as long as you're within the same subnet and not traversing any NAT/Firewalls - otherwise additional configuration will be required. Once the phone is registered, make sure the Google Voice/Chan Motif addon is enabled and create inbound and outbound routes for your Google account from that extension.
There are various resources available on-line which provide more complete step-by-step instructions on installing AsteriskNOW and configuring it for use with the Google Voice/Chan Motif addon. FreePBX also has their own community forums if you require any assistance with FreePBX or the Google Voice/Chan Motif addon: http://www.freepbx.org/forums
Also, here's where I downloaded AsteriskNOW from:
Unfortunately there is not, to my knowledge, anyway to directly register a Polycom phone directly to your Google Voice account. Back before Google purchased the Gizmo5 service I believe this was possible, but Google has since then disabled a lot of the direct SIP functionality that once existed with the service and re-worked the platform around Google Talk (now Hangouts). The Google Voice/Chan Motif addon interfaces with these protocols and not the SIP technology that Google Voice was built upon.
I'm not personally familiar enough with other services that bridge SIP registrations with Google Voice in order to offer much of an insight on any alternatives.
With that said, I wish you well in your endeavor.