Here is a complete answer. As se7six said, Groove IP ($5 on the Android market) is the only thing you need in order to make calls without using minutes (i.e. bypassing completely the voice network and using data instead).
You must have a Google Voice account and a Google Voice number. You need to configure your GV number to forward ALL calls to Google Chat.
Inside Groove IP, you need to enter your Google Voice user name and password. Groove IP will log in and register with the network. You will see a little green icon in the corner, indicating that Groove IP is working. To make a phone call using your data connection (instead of voice minutes), you use your regular dialer (or tap the name from the call log, or contact list). You will be prompted if you want to make the outgoing call via Groove IP, or via regular voice network. If you do it via Groove IP, the recipient of your call will see your GV number on the caller ID screen. If you don't, the phone uses your minutes, and recipient sees your regular mobile number.
Groove IP works reasonably well. Unfortunately, because it relies on data network, it is much less reliable than regular voice calling, because data coverage is much less robust than voice coverage. I'm in NYC and in many places, I get 1,5-2Mbps down and 450kbps up. This is plentiful for Groove IP, and sound quality is very good (actually better than voice network). However, very often, there is latency and sound is delayed by several seconds. Also, when I call someone, the other person can't hear me, while I can hear them perfectly well. Or they hear garbled noise. When you use WiFi as your data connection, Groove IP is muc more reliable.
Bottom line, you cannot replace ordinary voice calling with VoIP calls without sacrificing reliability and quality. More often than not, you'll be forced to fall back on the voice network, which is, by now, extremely robust. For me, Groove IP gives me reliable calls often enough to allow me to stay on the $25 plan without burning through my minutes. I still spend almost all of those minutes on calls when Groove IP failed to connect, or the other party couldn't hear what I was saying. Depending on where you use your phone to make calls, you may get better or worse results.
answered 4 years, 7 months ago
By using the app GrooVe IP you can place/receive free Google Voice calls that won't use your minutes.
answered 4 years, 8 months ago
Android 2.3 (Gingerbread) is the first version of Android to support VOIP natively, so this is a maybe when that upgrade comes out I guess.
answered 4 years, 11 months ago
Start with Sipdroid, Google Voice, etc. There's no one way, or easy way, to do this.
The Optimus is capable of using Google Voice. However, the Google Voice app will use your plan minutes.