It is now operating more than six million lines, both fixed and mobile, making it one of the Czech Republic's largest providers of fully converged services.

Previously two companies, fixed-line operator Český Telecom and mobile operator Eurotel, it was acquired by the Spanish company Telefónica in 2005 and merged into a single legal entity and given its present name on 1 July 2006.

In 2004 it launched CDMA/1xEV-DO broadband wireless service (data-only) at 450 MHz, leveraging its legacy NMT network.

[citation needed] On 1 June 2015, O2 Czech Republic has been separated into two mutually independent companies.

[4] The controversial business conduct of O2 Czech Republic with its retail and business customers, including anti-competitive practices and other questionable activities, has led to concerns due to its aggressive tactics, resulting in several legal disputes.