Trials have started of a national roaming SIM that will be commercially available before spring 2015. The SIM is being tested by 24 Severn and will allow customers of one operator to use another operator's network when their own network does not provide a signal.

This could be the answer to the UK's rural 'not-spots', large areas of the UK where mobile network coverage is not available or very limited. In an attempt to help tackle the issue, 24 Seven has set up an MVNO agreement with mobile network operator (MNO) O2, but its specially-developed SIM will jump onto either EE or Vodafone if it cannot find the O2 network.

The Government raised the issue of national roaming late last year and had hinted that network providers would have to open up their networks to national roaming.

The various companies objected strongly to the idea which was subsequently dropped by the government. However, instead, the network providers will be held to a £5bn infrastructure investment commitment