Mobile phone users in Nigeria can now keep their old number when switching services, a major shakeup in the West African nation's lucrative telecommunications market where customers often complain of poor service.

The service, pushed by the federal Nigerian Communications Commission, began Monday across the nation of more than 160 million people. Under the service, customers can switch providers every 90 days and keep their number for free.

At risk most in the new service is South Africa's MTN Group Ltd., which holds the majority market share in Nigeria, but faces increasing problems with poor service and attacks on its equipment. Brett Goschen, CEO of MTN's Nigerian subsidiary, told The Associated Press that the company likely would lose customers in the short term.