I just blogged about i2Telecom's "Cellular Bridge" feature that let's you pick up your cell phone, dial the i2Telecom InternetTalker, and the device will recognize your CallerID and give you "2nd dial-tone" to dial another phone number.
Well, coincidentally, a source has just told me that Level3 and Verizon are working on a similar feature that will let you dial your home VoIP phone (Verizon's VoiceWing VoIP service I assume), it will detect the CallerID, give you 2nd dialtone, and then let you make an outbound call.
Apparently it will only cost $0.12 PER CALL! (not per minute.) I'm not sure if this is U.S. only or international as well. I'd be damned impressed if it were $0.12/call internationally, but that is highly unlikely.
I should mention that most cellphone plans have "free minutes" in a bucket that you would be using up to call your home VoIP number -- which you are then charged $0.12 per call. It really only makes sense if you will be paying more money by dialing directly from the cellphone than over the 2nd dialtone. In most cases, that would require an international call, but not always. Some cell phone carriers offer unlimited regional plans - i.e. if you are dialing a number in your region it's free. So using this feature would allow you to dial outside your region for free (assuming you are in the region when you dial from your cell phone into your home phone)
Certainly, using your cellphone to call home's VoIP line and then calling internationally does make a lot of sense. For one, VoIP rates are much lower than an international call made from a cellphone. You'll probably even get better voice quality too using VoIP rather than PSTN since international PSTN calls often goes over satellite which has a lot of latency.