Nokia, the world’s biggest maker of mobile handsets, threw its weight behind internet telephony on Monday in a move that could divert large volumes of voice traffic from cellular networks and put further pressure on mobile voice tariffs.

Jorma Ollila, chief executive of the Finnish group, unveiled Nokia’s first mass market dual-mode handset, the N6136, which will work on both an operator’s mobile network and switch to a fixed-line broadband connection when it is within range of a Wifi hotspot.

Mr Ollila said the phone’s software would be capable of supporting a voice-over-internet-protocol, or VoIP, client enabling a user to make calls at much lower cost when connected to a fixed broadband link than over a mobile network.

“Internet voice is going mobile,” Mr Ollila said as he released details of the handset, which at €275 ($327) is significantly cheaper than Nokia’s only other handset that will support the service.

Nokia does not so far have any customers for the service, as operators continue to work on how a dual-mode business model might work. But he said there were “US and European operators who want to be the first one”.

BT, the UK-fixed line operator that piggybacks on Vodafone’s network in the UK, launched a dual-mode fixed/mobile phone late last year with Motorola but so far it does not support VoIP.

The technology Nokia is using allows the operator to retain control over which type of VoIP service a subscriber can access.

There is growing concern in the industry that with the growth of Wifi hotspots in many urban centres, mobile networks are increasingly vulnerable to dual-mode handsets accessing cheaper fixed-line services.