Esat Digifone
Esat Digifone, a GSM mobile phone network which was the first competitor to Eircell (then a Telecom Éireann subsidiary) was originally a joint venture between Esat Telecom and Telenor, however when Esat was sold to BT, the mobile division became part of BT Wireless, which was eventually spun off as O2, which in turn was bought by Spanish-based Telefónica in 2005 (EU approved in 2006). The company is now officially registered as Telefónica O2 Ireland Limited, but trades as O2.
Read more about this topic: BT Ireland