Ofcom has set the deadline for mobile phone number portability at two hours from September 2009, down from the two-day limit set to come into force in April 2008.
Number portability allows subscribers to retain their number when switching from one provider to another.
Under the new rules, consumers will be able to receive calls using their existing number within two hours of moving to a new mobile network. The current system takes five days.
In the past, number porting was often carried out simply by forwarding calls from the old network to the new provider.
"These rules will make it quicker and easier for consumers to keep their number, thereby strengthening competition and consumer convenience," said Ofcom in a statement.
"It will also help to protect consumers from the risk of losing calls if their old provider's network fails."
"In the review of the current European framework, the Commission proposed a maximum of 24 hours for operators to move their number to new providers," said Ovum analyst Matthew Howett.
"It is hard not to see Ofcom's decision as partly a knee-jerk reaction to this proposal."
Howett did praise the switch to an industry database, which he claimed would remove dependency on the previous network.
"The new database will make it possible to route calls to ported numbers directly to the new provider's network without the need for the call to travel over the previous network," he said.
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