Using Rynga

Just follow slow_quick's instructions and configure Generic Service Provider as the following:

Configuration Name: Rynga
Make This the Primary Line to Call Out from: unchecked   
Voicemail Notification(Optional): checked
7-Digit Dialing for USA & CAN (Optional): leave it blank
Use This Service for Emergency 911 Calls: Unchecked
Service Provider Proxy Server:sip.rynga.com
Service Provider Proxy Server Port:5060
Outbound Proxy Server:leave blank
Outbound Proxy Server Port:5060
User Name: Your Rynga username
Password: Your Rynga password   
URI: leave blank

You need to have a Rynga account first.