Using Google Voice with SPA2102 or other ATA

MySense

IPKall is still free but you may have to try several numbers before you get one that isn't orphaned on an account somewhere.
http://phone.ipkall.com/

A simple option would be to use the obi http://www.obihai.com/googlevoice.html

Simon Telephonics
https://simonics.com/gvgw/
https://simonics.com/2012/03/setting-up-a-linksys-pap2-with-the-google-voice-gateway/

Google Voice/SIP gateway tutorial

Setting up a new gateway
Step 1: fill out the form, following the prompts and reading the FAQ below for additional information. Then click the Add button.

Step 2: GVGW will test your account and then present SIP authentication and registration information that you will use to set up a SIP trunk to the gateway.

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Deleting your Google Voice gateway
Step 1: fill out the form again, using the same information you filled in to add the gateway. Note: this time, you do not need to enter an e-mail address. Then click the Delete button.

Step 2: GVGW will confirm your configuration and proceed to log out the Google Voice user and delete the gateway registration.

Usage
Important: If you have never made a call through Google Voice before, you must first log into Gmail chat with your account and initiate a call through the chat widget. Then log into Google Voice, go to your voice settings and select Google Chat as the destination for call forwarding.
Configure a SIP trunk and register your system to the gateway address given in your Add confirmation. You could also just register a single hardware phone, softphone or ATA.
You will receive incoming calls over SIP to your Google Voice DID. To place calls, send your calls over the trunk using a full 11-digit (1-areacode-number) string for US calls. If you have credit on your Google Voice account and want to send international calls, use the full international dialing string starting with the country code.


Setting up a Linksys PAP2 with the Google Voice Gateway

Thanks to Hans for a quick note on how simple it is to set up the Linksys PAP2 with Simon Telephonics’ Google Voice Gateway.

Start by returning the adapter to factory defaults.
Referring to the settings page that appears when you have successfully registered your Google Voice Gateway, configure the PAP2 as follows:
Line1 on Linksys PAP2  
Proxy and Registration
Proxy: Server
Subscriber information
Display Name:   Your name
User ID:              Username
Password:           Secret
Use Auth ID:       Yes
Auth ID:              Username
Make sure that the Info page shows the line1 status/registration state as “ONLINE.”