There are 188 telephone exchanges in London and all offer ADSL internet services. Most of London, and some adjacent places, are covered by the 020 area code. Some parts of outer London are covered by the 01322, 01689, 01708, 01895, 01923 and 01959 zip codes. There is extensive wireless LAN coverage, especially in central London such as the City of London Corporation, who are developing blanket coverage for the financial district. There is wide coverage from five mobile phone networks of which four are GSM/UMTS and one is UMTS-only.