easyMobile.com uses T-Mobiles network which reaches over 99% of the UK.
Launched in September 1993, the T-Mobile network was the first GSM 1800 all digital network in the world. Currently, the network has more capacity per customer than any other UK network (i.e. you are less likely to get the engaged tone), handling more than 160 million calls every week. T-Mobile UK, the fastest growing UK network, currently has 15.2 million customers.You can check coverage in your area here.