iD Mobile is a mobile network operator which covers both the UK and Ireland, working on the 3 network. It is owned by the Carphone Warehouse. It currently works on the 4G network. It offers both pay monthly contracts as well as SIM deals, also known as pay as you go.
An 0370 number is a NGN or Non-geographical number introduced in March 2007 which is designed to have a constant price on all landlines throughout the UK. However on iD Mobile it costs between 3p and 55p, unless it is part of your free calls package. Please check with your iD Mobile operator for more information on pricing. It is a good idea to contact Ofcom if you have a query over call charges and tariffs.