Telefónica Slovakia is a provider of mobile service O2 in Slovakia. Telefónica started in Slovakia with commercial services on 2 February 2007 with about 600.000 preregistered users, and ~400,000 Slovaks actively using the O2 service. The operator has 781,000 active SIM cards to date 30 September 2010. The company is subsidiary of Telefónica O2 Czech Republic, part of the Spanish group Telefónica Europe. Users are identified by prefix 940, 944, 948 and 949 in mobile number. Telefónica Slovakia, s.r.