Let me say this aloud: VoIP is the future of A/V communication.
Sure, there will always be alternative ways as a backup technology (e.g. satellite, GSM) when short-range communication is not available, but VoIP via WiFi or 4G or WiMax or whatever is the next big thing, will have to eventually take over. It makes logistics and common sense.
Right now, the 3G and 3.5G data networks are not very good in terms of latency compared to pure 3G/GSM voice, but once this stumbling block goes away, even the carriers themselves will have to move to a more "software-based" solution for voice calls, something that will resemble today's VoIP technologies.
Google Voice is not itself a SIP VoIP service, but it's a service that definitely helps you spend less money on communication. I wrote a review of the service here. Needless to say, I am enthusiastic about it.
Right now, having Apple blocking this innovation and natural progress does not look very good to my eyes. Apple said that the various Google Voice applications "duplicate functionality" and hence they were not authorized. But really, this is just hogwash and a poor excuse for the inexcusable. Google Voice allows for CHEAPER phone calls, so I don't see how this is "duplication" of anything other than having a screen with buttons that range from 0 to 9. The service offered is not the same.
Another thing that's bugging me with Apple's iPhone is that it doesn't allow for background applications, and so I can't have any VoIP or IM application running on the background. PUSH is not the answer for everything, because by the time you get a PUSH message, load the VoIP app, register to the SIP server, and try to answer a phone call, the other party might have already hang up. It feels a lot like someone is giving you a can full of tuna, but with a stone instead of a can opener.
I really do hope that the situation resolves and Apple allows VoIP and Google Voice apps to be freely installed on their system. And why not have a native Apple implementation of a SIP client, just like on most Nokia S60 phones, which is fully integrated to the UI of the phone! It'd be like heaven!
As for Google Voice in particular, it is one of the best thing happened recently: it allows me to call my mother in Greece for $0.02 per minute! Cheaper than any SIP provider or Skype! If Apple (or more precisely, the carriers) want to take this away from me they will have to try harder than that. And besides, why all the Google Voice hate? Why Skype gets a free ride on the iPhone?!?
Google Voice rules, and I only hope that Google goes ahead with it full speed, and even introduce a full SIP server (rather than having to use Google Voice with VoIP via the lagging Gizmo5 service). If the iPhone doesn't want to play nice with VoIP in general, I definitely see an Android or a Nokia SIP-capable phone in my future.
Hey, all I want to do is to just call my mom without getting robbed. Is that too much to ask in the information and communication age?