SOME Mexican telephone customers couldn't complete calls easily on the first day users were able to retain the same telephone numbers when they changed carriers.

Telefonos de Mexico SAB, the country's largest fixed-line carrier, said its own network is working, though users of other phone systems in 38 cities across the country might not be able to make some calls. Mexico's Federal Telecommunications Commission said the start of the new telephone number system was "satisfactory" and that any call interruptions would be eliminated within 15 days, Bloomberg News reported.

Number portability, as the new regulation is called, allows users to change phone carriers and keep their numbers. The change will lead to better service and reduced costs, the Federal Telecommunications Commission said on June 30. About 5,800 phone customers requested a change in service while keeping their telephone numbers, the Commission said. The first 36 requests will be connected to their new carriers early today, the commission said.

Telmex, as the former national phone monopoly bought by billionaire Carlos Slim in 1990 is known, received reports of difficulty completing calls by customers of other carriers.