It doesn’t look like embattled VoIP provider Truphone is going to get much backing from the UK communications regulator in its tussle over termination charges with T-Mobile.

On Monday, the VoIP provider complained that T-Mobile had started blocking connections to Truphone’s new 07978 number range.

T-Mobile argues that even though Truphone has managed to acquire a number range typically reserved for mobile phones, it is not in fact a mobile operator, and should not receive the termination charges normally given to mobile carriers.

On the one hand, this seems reasonable as Truphone terminates calls to it users on a fixed (wifi) network. But on the other hand, if a Truphone user is out of range of a wifi connection, Truphone has to route the call through to the user’s mobile number and must pay to terminate the call on a mobile network.

A spokesman for Truphone told telecoms.com that T-Mobile is only offering Truphone £0.021 to terminate a call on the VoIP provider’s service – the same price it pays BT to terminate a call on its fixed network.

But it costs Truphone £0.09 to terminate a re-routed call on a mobile network and an average of £0.0611 to terminate all calls.

Ironically, this means a T-Mobile subscriber could call a Truphone number and T-Mobile would pay Truphone £0.021 to terminate the call. But if the recipient is not on a wifi connection that call could then be re-routed to a mobile network – possibly T-Mobile’s – and then Truphone would have to pay £0.09 to terminate that call.

The crux of Truphone’s argument is that it would lose money on every call and its business would become unworkable if every operator took this stance.

However, Ofcom is not likely to weigh in on the matter. A spokesman told telecoms.com that the dispute is “a commercial rather than a regulatory issue” and it was up to T-Mobile and Truphone to sort themselves out.

Crucially, Ofcom does not recognise Truphone as a mobile operator, regardless of what ever number block it uses. “Call termination regulation only applies to the four GSM operators [T-Mobile, Orange, Vodafone and O2] and 3,” the spokesman said.

With the net neutrality debate raging on in the background, the fact that Voice over IP has been given such short shrift by the mobile carriers has made it something of a volatile topic.

Earlier this week, telecoms.com spoke with Roy Timor-Rousso, VP of product marketing for mobile VoIP service, Fring. Fring is another likely target for the operators as its strategy is to provide end to end IP voice, whereas some of its peers, like EQO, use the circuit switched network to complete the call and the IP network for signalling.

But Timor-Rousso does not believe this is the case. “Operators are not stupid,” he said, “They will leverage VoIP as a complementary technology. One way of reducing churn is to bundle VoIP into the package along with data and voice,” he said.

But at present, many mobile operators, T-Mobile included, expressly ban the use of VoIP or peer to peer technologies on their data networks, effectively dispelling the threat of VoIP as a rival voice service.

Timor-Rousso conceded that operators may see their own brand of VoIP service as less dangerous and controversially, these same operators are also quietly investing in their own home grown, or bought in VoIP platforms.

Last month, Deutsche Telekom’s investment arm, T-Online Venture Fund, announced an investment in internet telephony player, Jajah. The T-Mobile parent then said it expects to bring Jajah-based web embedded solutions to consumer and business customers as a result of the partnership and most likely under its own brand.

At present, T-Mobile UK does allow users to make VoIP calls via any provider as long as they subscribe to the Web ‘n’ Walk Max plan at £57.50 per month.