@A price issue
Nothing to do with pricing.
1. I am typing this off a laptop with a cellular modem travelling between Cambridge and London (dead in the middle of the "civilised" part of the UK. There is 3G coverage on under 20% of the route. Rest either has none or has only GPRS (no edge due to Voda's infinite wisdom). This is so far away from being useable for VOIP it is not even funny.
2. The 3G bandwidth allocation model is very good as far as allocating channels to voice over 3G. It sucks bricks through a thin straw sidewise as far as multiple data clients are concerned. The network neither has the capacity, nor the scalability to support a large number of VOIP clients (even with HSDPA which does not change this part of the MAC layer).
3. The IP layer QoS is not interfaced into 3G MAC layer QoS so while technically possible VOIP will suffer from horrid dropouts once the network gets loaded (once again, someone needs to look into the data model for 3G instead of listening to too much marketing whale songs).
4. The Round trip time on 3G in in the UK is firmly in the 200ms + twilight zone. As a result any calls to another similar client, transatlantics, or even to cellular will have noticeable delay.
5. The networks are currently mostly NAT-ed behind a single address or small address pool. While this may work fine for now it will get very entertaining with a lot of VOIP connections as far as resources are concerned (unless the operator puts local VOIP servers).
And so on. Frankly, unless 4G rewrites the book on the way the MAC layer is used and allocated to devices over time VOIP 3G is dead on arrival.