Android and voip - is this possible?

[computerpro3]

This might be a very stupid question, but I've searched and I've not found a clear answer to it. I'm new to Android so I have no clue.

My goal is to be able to have me and my girlfriend be able to call each other over VoIP. We are on different networks so the minutes add up quick. I have a Incredible pre-ordered and she's getting an Android phone shortly.

I've gathered that there are ways to make free VoIP calls, but what I can't figure out is if it's possible for it to function just as a phone does. My girlfriend is a bit afraid of technology and I need this to be dirt simple for her so she doesn't give up on the whole idea (and blame me for it).

In other words, I want to be able to launch an app on my phone, dial her google voice number, and then have her phone ring and connect automatically via voip so no minutes are used.

VoIP is great, but she won't go for it if we have to "pre-plan" our calls - "Hey honey, please launch your voip app so we can talk". Launching an app to dial outgoing is fine, she can handle that. But how it would handle the incoming calls is the critical part. It needs to be able to work, and work automatically via voip through google voice (or something similar).

Is this even possible on Android? Any help would be greatly appreciated.