Both companies accuse BT of anti-competitive practices in contravention of the Competition Act 1998 and Article 82 of the European Treaty.
Specifically, they allege that BT has been pricing wholesale end-to-end calls to resellers at below cost since April 2005, with the deliberate aim of driving down the margins for competitors – like Thus and Gamma – and consequently putting them out of business.
Ofcom's investigation will decide whether BT has abused its dominant position in the wholesale voice connections market.
While Thus is the telco spin-off of Scottish Power, formed in 1999, Gamma, founded five years ago, focuses on selling telecom services to small businesses.
The complaint has been supported by Cable & Wireless.
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