it uses a sub channel, it goes when the traffic is light, it is little in the way of bandwidth, but it is charged at an exorbitant rate... and we the dumb consumer pay it!

Voice is critical as latency can be an issue... so it should have the highest network priority.

Data can be packet reassembled at either end, and should be cheaper... but the bandwidth demands and the phone company thought process of charging by the minute, tend to hamper data.