Mobile/Wireless operator T-Mobile has taken the extraordinary step of banning Voice-over-IP (VoIP) from its super-3G data (card) network (HSDPA), apparently highlighting low quality as the reason:

Initially it said the move was a "commercial decision" and such services were "not key" to its customers. But in a statement issued on Wednesday, T-Mobile said instead that VoIP technology "is not yet of a consistent or high enough level of quality to offer a good customer experience on the T-Mobile network".

"This situation may change in the future," it said, "but for now we believe it is in the best interests of our customers to restrict the use of VoIP technology."

Telecoms analyst John Delaney of Ovum said T-Mobile’s decision was "not entirely illegitimate". "Technical reasons make it difficult to offer consistent services," Delaney stated on Thursday, suggesting that VoIP’s bandwidth-hungry nature is one reason behind T-Mobile’s decision. "The main reason operators are concerned about VoIP over their 3G networks is not so much a worry about substitution of calls and call revenues, but degrading the performance of the network for other users."

The move sounds awfully familiar to the way in which a good number of UK ISP's now block or restrict P2P applications. In this case we're sure that it also has nothing to do with VoIP being a competitive product to their own voice services *cough*.

ISPr note's that no other UK network prohibits the use of VoIP with data cards and some have even signed deals to grow services around it. More @ ZDNet.