T-Mobile has denied that it is blocking a VoIP firm from receiving calls from its network.
T-Mobile is not currently allowing calls to the 07978 8XXXXX number range used by VoIP provider Truphone.
Other mobile phone companies have all agreed to connect to the Truphone network and the company claims that T-Mobile is trying to block VoIP "as a matter of policy" while it develops its own VoIP services.
"It is a complete red herring that we are anti-VoIP," said Simon Marks, corporate communications manager at T-Mobile.
"Truphone has some of the highest termination rates in the industry. We feel they are not fair and reasonable given their costs and we are trying to sort of reasonable rates."
Marks said that T-Mobile was in communication with Truphone but felt that as a VoIP company its costs should be lower than average and that the rates being asked for were too high.
"T-Mobile will argue that it is not 'blocking' Truphone but is merely negotiating on price," said Truphone chief executive James Tagg.
"T-Mobile receives 35p per minute from its customers but is offering only 0.21p per minute to Truphone even when Truphone's costs are 9p per minute to terminate the call.
"T-Mobile is blocking our numbers unless we accept this loss-making offer and, since T-Mobile is the only company that can route calls from its customers, it has a complete veto on the Truphone service."
Tagg claimed that T-Mobile was trying to abuse its position and said that such a move would "put telephony back 100 years".
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