London NHS trusts are signing up to tap for free the voice over IP capability that was recently added to the NHS's N3 broadband network.

The VoIP offer, which network provider BT is calling a "large-scale pilot" to promote the network's new capabilities, means that London trusts that sign up are connected to the N3 Local Gateway Service for nothing. Using VoIP enables all linked-up trusts to call each other for free. They also benefit from a nationally negotiated reduced tariff for mobile calls, through to a partnership deal with mobile network operator O2.

So far 21 London trusts have joined the pilot, with another 26 ready to proceed. Several more are expected to sign up before funding expires at the end of the year.

North West London Hospitals NHS Trust was the first to sign up to the pilot, and went live in October. Rick Juniper, director of ICT at the trust said converging the trust's voice and data over one single network "presents a significant opportunity for us to quickly reduce our telephony costs."

He said most of the Trust's call charges from landlines were spent on calling mobiles and the offer of nationally negotiated rates for fixed to mobile calls would "lead to substantial savings."

NHS Connecting for Health, which paid for the original installation of the N3 network as part of the NHS's £12.4bn National Programme for IT, has part-funded the pilot with BT to explore the benefits of the N3 Local Gateway Service across a large-scale community.

Under the "free" offer, costs to trusts are limited to the provision of a suitable signalling interface card to connect to the N3 Local Gateway Service, software configuration charges and a monthly management fee.