O2

Originally called BT Cellnet, O2 (www.o2.co.uk) is just one step behind Vodafone in terms of subscriber numbers, with just under 15 million customers in the UK.

Running both 900 MHz and 1800 MHz GSM technology, O2 is available across 90% of the UK, reaching 99% of the population. O2's 3G service went live in February 2005, originally providing cover for 20 cities. 3G is now available to over 50% of the UK population, with coverage improving all the time.