My idea is get rid of minutes and text and simply have data on your phone. Then you can use the call/sms service of your choice to provide those features over https. Basically unbundle the whole deal. The carriers would never go for it but I think it would work.

I've got a nephew who sort-of does that with an iPod touch. It doesn't even have a cellular data connection - he relies on glomming on to free wifi at school/home/friend's houses/the library/the shopping mall/wherever, and gets iMessage and Skype only when he's got wifi - which is "good enough" for him to not even bother upgrading to a phone with a pre-paid account... (He's even managed to convince his Mom to leave the wifi hotspot on her phone running all the time, so he can make/receive calls in the car...)