This sounds like spin by a non CDMA proponent to me. The fact is that on any given tower there is an allocation for voice and data not voice, data, and voip. Voip looks and feels like data as it is voice encapsulated in an IP data packet and is not differentiated by the contents of the packet by the radio tower. The radio can go to a standby state after a period of inactivity which is a reasonable expectation given the limited nature of frequency allocation and could potentially have an impact with some poorly implemented applications. A savvy network engineer can mitigate these issues. You can be sure that other standard over the air radio allocations will have the same issues.