In this day and age it is unbelievable that everything isn't treated as just data. Texts, phone calls, internet usage etc should all be charged and the same rate. ie - pay $XX per month for unlimited (or capped at XXgb) and we don't care what type of data is used as that's all it is - data.
Packet-switched networks don't work well for real-time communication: you need circuit-switching. 'Voice' channels on mobile phones provide a special type of connection (granted, it may be packet-based fundamentally) that you can't get with a 'pure' IP.