Mobile network operators will have to provide the porting authorisation code (PAC) that mobile phone users need to switch operators within two hours from 11 April 2011.
A spokesman for Three said Ofcom's decision had "failed UK consumers". It said nowhere else in Europe did consumers have to ask for their code. This made it harder for them to take advantage of better offers as and when offered.
"Fast, easy, recipient-led mobile number porting is the fundamental platform for choice and competition in the mobile market," a Three spokesman said. "The porting system that Ofcom proposes to keep makes it difficult for customers to choose a deal that suits their needs."
Ofcom's new regulation requires operators to transfer mobile numbers in one working day rather than the current two days. The operators will have to issue the PAC either immediately over the phone or within two hours by text message. Some operators now rely on the post to deliver the code, which can take several days.
The move is a sequel to an earlier victory by Vodafone against Ofcom's 2007 proposal to move from two days to two hours to provide the PAC.