O2 Slovakia is a provider of mobile service in Slovakia. O2 started as Telefónica 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 1 700 000 active SIM cards (3 month activity) to date 1 September 2015. The company is subsidiary of O2 Czech Republic.