The government on Wednesday said telecom regulator Trai has issued showcause notices to Bharti airtel, Idea Cellular, Loop Telecom, Reliance Communications and Vodafone over alleged violation of mobile number portability regulations.

"Trai has received complaints from some customers regarding wrong rejection of porting requests by telecom operators. They also came to know through media regarding Rs 10 being charged for a message (SMS) for requesting porting code through number '1900'," Minister of State for Communications and IT Milind Deora informed the Lok Sabha in a written reply.

Trai had issued a directive to all cellular mobile telephone service providers and unified access providers on December 3, 2010, prohibiting extra charges for SMSes sent to '1900', the number for availing the MNP service.

Regarding outstanding payments due from the subscribers availing the MNP service, Trai recommended that if the unpaid amount in the previous bill is less than Rs 10, the service provider may include the same in the subsequent bill of the subscriber without any penal charges, he added.

In order to reduce the number of porting rejections by service providers, Trai had issued directions to the service providers on May 24, 2011, specifying that rejection on the premise of contractual obligation can be done in case of post-paid connections with bundled handsets, or corporate connections, which have an exit clause that has not been complied with by subscribers, Deora informed the Lok Sabha.