The company, which has a legal department based in Bristol, has previously used the local firm for property and planning work and the magic circle firm for corporate work.
But on its acquisition of Ananova, the world's first internet newscaster, it decided to instruct Burges Salmon. The mobile phone company paid £95m for the information provider from PA New Media, the interactive division of the Press Association.
Senior in-house lawyer Chris Groves says that Orange decided it was time to give Burges Salmon a try and was very pleased with the service it got.
He says: "Burges Salmon does a lot of work for us on the planning side and on property so we know those partners well. We wanted to explore its corporate side and Alan Barr [corporate partner] was introduced to us.
"It wasn't just financially motivated - the level of service is as good but the accompanying contact that you can have with the team, including the partner in charge, is probably better."
Groves says that he will use Burges Salmon again for similar transactions.
Slaughters head of corporate Nigel Boardman, who advised Orange on its acquisition by Mannesmann, says it makes sense for the company to instruct two firms. "We would have been happy to do [the Ananova deal] but we are equally happy that it went to Burges Salmon," he says.
The team working on the deal was led by Barr, with commercial partner Simon Coppen and tax partner Nigel Popplewell.