I picked up an ebook with a pretty straight-forward method. I myself know a better method, but this one is working, too.
A little bit much of a hassle though. I'll just dump it here:
Step 1. Put your browser to private/incognito/inPrivate mode.
Step 2. Sign up for a free account in callcentric.com No need to provide real information just insert a working email. Verify your account and after that take note of your "Callcentric #:" that is the only thing you need from here.
Step 3. Signup for a free account in phone.ipkall.com. Use the same email address and password that is accosiated with the callcentric account. And insert your callcentric # to the SIP URI field. Insert in.callcentric.com as the hostname. Select the areacode for your virtual phone. They are all good.
Step 4. Click the verify link on the verification email ipkall.com sent you and take a note of your phone number and you are done.
Step 5. Configure your SIP client. I recommend this:
http://microsip.org.ua as it is really easy to use. You can also install SIP client to your smartphone. Just search appstore for SIP-client.
Sip Server: callcentric.com
User: 1777231315 (that callcentric id from step 2)
Domain: callcentric.com
Password: your password
Optional:
Step 6. Launch that SIP client you installed.
Step 7. Make your first google account and verify it with your US ipkall number. Phone call only
Step 8. Download and install Hotspot Shield to be able to set your location to USA one. Run the hotspotshield and check that your IP is located in USA
http://whatismyipaddress.com/
Step 9. Open voice.google.com in your web browser and sign-in with your Google account. Choose an phone number and verify it with your SIP-client. And after that you have google voice number that can receive SMSs and calls for free.