This guy made a VoIP over EVDO phone call in his car using Vonage. Good stuff! I love this quote: "I got some really strange looks as I held this old fashion POTs line to my ear while parked in a parking lot. People walking by probably thought I was on the strangest cell phone ever." 
For his tests, he used the following to make Vonage calls:
- Compaq Presario
- LinkSys RT31P2 VOIP router (included with VOIP server)
- Crossover Ethernet cable (need this if not using a router)
- Old fashion dialtone phone
- Radio Shack power Inverter, power for the router in the car
- EVDO Antenna (External Booster Antenna)
- EVDO TurboCharged PC 5220
He also writes, "It will be interesting to see how cell phone companies handle this technology - especially as cell phones come standard with EVDO. Why? When placing VOIP calls over EVDO, the cell phone companies do not charge you against your plan or
minutes - so it is a way to make unlimited voice calls. I don't think they will like that too much."
Good point... Although, I bet the carriers would be ecstatic if you paid $30-$50 per month for cellphone voice service and another $70-$80 for a EVDO data plan.
Check out the VoIP over EVDO article.
Update: I've successfully made my own VoIP calls over EVDO, including Skype, fring, and SIP-based calls. :)
