Ok guys - I know that this works on my Evo, and I will install it on my 101 when it gets here. But I wanted to put this down to see how it works for you.
This is taken from:
VOIP for Android devices
1. If not already done, install Google Voice on your device using the link already on this thread above.
2. Install Sipdroid from the Market on your device. Alternatively here is a link to it -
Sipdroid
3. When you run the Sipdroid app for the first time, you’ll see a touch button at the bottom of the screen. This will setup Sipdroid, a background service at a site pbxes.org (a free virtual PBX site), and activate the VOIP service. You be prompted to enter your Google Account User ID and Password. This info is used to create an account at pbxes.org. This service does background/transparent call management.
4. Sipdroid will auto activate when you turn on wifi and stays active until you disconnect from wifi. There will be a new icon (Round icon which should be green when connected) in the notification area of your device showing if you are connected to the VOIP service. Close out of Sipdroid - I haven't used it again after successfully signing in.
5. Install fring from the Market. You'll use this to initiate GV/SIP calls over wifi.
6. Setup your SIP account on fring - make sure your entire pbxes.org address is used as the login.
7. Make sure that it successfully logs in, and then press menu and open the dialer. Enter in a phone number to dial, and choose "SIP call". I entered in the phone number with area code but no "+1" or "1" in front.
That should be all you have to do. Let me know if it doesn't work and we can troubleshoot. I will be getting my 101 soon and then I will be able to test this.