I was once at a sales presentation where someone borrowed my GSM modem and used it for less than an hour. He was just trying to load a web portal. Bill came up to $600. My carrier called me in the afternoon to make sure that was me.
Typically a VOIP stream is between 2400 and 9600 baud, or 300 to 1200 bytes per second. At E0.25 cts per MB for instance that would make their voice tariffs look ridiculous and people would switch en-masse to VOIP.
They can't really win this one, either people will not use their data networks and they end up in front of the anti-competitive agencies (OPTA etc) or they lose a pile of money on their voice side.
Sucks to be them.
It is a fear I find to be mistaken. Even though a bit is a bit any way it is transferred, things like latency, jitter, guaranteed throughput, those are things that do make a difference to applications.
If I was a telcom company, I would start to write android applications that besides providing VOIP and streaming video, etc, also would set up these connections to use a QoS level that the subscriber would have as extra charge add-ons to their account. QoS might require lots of technology on the server side that isn't there yet.
If I was an evil telecom company, I might even introduce jitter on non QoS and make VoIP completely crappy quality. Making people that pick this route sound like real cheapskates. Aren't you glad I am not a telecom company?