It sounds like you are doing exactly what I did. It took a while to get it right, however. Here's what my set up is:
1. My "published" phone number(s) (I have a home and an business #) are Google Voice Numbers.
2. I bought and registered 2 localphone incoming numbers (DIDs). One for home and one for business. (I have an Obi 202, so if you have a 100 you would only have one phone, and I assume one incoming phone number so the rest of this explanation covers just one number).
3. In Google Voice, of course I forward calls from the GV# to my new Localphone number. So you DONT have to port anything to Localphone. (That way if you get tired of Localphone you can try a different provider.) The other benefit (to me, anyway) is Google Voice has excellent voicemail and call handling features. So I prefer to use GV Voicemail.
4. The OBI set up (I assume you have GV on SP1) is you set up SP2 for Localphone. That way you can fiddle with the settings without wrecking your phone service. To tell OBI you have a new service provider click on approved service providers (on the left) And from the bottom of the page click on Obitalk compatible providers. You may have done this. If you get an instances full message, you have to delete one of your existing setups before it allows you to create a new one.
5. Once you've added localphone, go back to the setup for the SP2 (assuming thats what you added) and check a couple fields.... Primary incoming and outgoing line. Check or uncheck as you prefer, keeping in mind that as long as Google voice is active (on SP1) you may need to uncheck those boxes to test your new setup.
6. I had to make sure that i input the localphone sip User name as my new "Internet Phone#" that localphone gives you. It is not the account number. Make sure you enter the localphone password from the INTERNET number. (I renamed all my localphone (account and sip) passwords to the same thing to make it easier to implement. So that's it for OBI set up.... Now let's go back to Localphone....
7 Localphone setup: Log In to your localphone account. I assume you have an incoming DID and put cash in the account. (I did not use auto-top-off since I was not sure it would work and I wanted the ability to bail out with minimum hassle.)
8. My Account / Settings will show the basics of your account. Nothing really useful here... just admin stuff. But DO make sure you add a registered number (specifically your Google Voice number) They will verify that number by calling it, so make sure your Google voice number is still operational.
A useful starting point is this:
http://www.localphone.com/dashboard/local_numbers.
(a) Click on Internet phone to see your internet phone number: (7 digits)
(b) Further down on the page is your SIP ID (=the 7 digit internet phone#) This number is used for Obihai.
(c) Next SIP Password (which you can change as mentioned before)
(d) Call Forwarding (should be INACTIVE) To make it inactive, click change and make sure all the boxes (regarding localphone voicemail are unchecked) Recall I use Google Voice as my front-end for voicemail.
(e) Caller Id - Change THIS to use your registered Google Voice number (that way when you call someone your Google voice number displays).
(f) Active devices - It should refer to your OBI device. If not, then make sure you have set up the OBI to use Localphone.
I guess my final thoughts are these: It took me - (a newbie, but determined) several days to get it right. And you really have to go back and forth between both OBI, Google, and Localphone multiple times to get it to work. Outgoing was easy, but for me incoming was much trickier.
Good luck.