As far as I can tell, the google voice app for the iphone uses the Apple Push Notification Service, so I don't think it is going to be possible to use that to push sms messages to the phone. The android app also uses a similar system. I have looked around a bit, and played with the different google voice websites, and all of them use some sort of polling system to get updates.

The only way I can find to get push notifications to work would be to utilize some sort of optional server (either created specifically for this, or using something like gvmax, or voicegrowl). GVMax and voicegrowl require you to forward your sms emails to them, and then they send out some sort of notification to your device (http post, howl, or prowl).

I would love to be wrong on this, but I have done a fair amount of research, and haven't found anything.

MQTT is supposed to be "extremely lightweight" way to accomplish push messaging, and they provide clients in a lot of different languages. What about making a server app that pushes notifications to the device? I realize this isn't as elegant, but I don't see any other way. I have a week off after exams, and would take a shot at making something like this if you are interested.