Singapore's fourth telco TPG Telecom sparked a war of words after accusing market leader Singtel of blocking number porting requests from subscribers looking to switch.

TPG, which launched mobile number porting on Feb 5, said in a Facebook post on Friday afternoon that Singtel had "repeatedly denied all valid porting requests to TPG".

Porting allows customers to keep their existing numbers when switching mobile plans from one telco to another.

"This affects consumers' freedom of choice and we have raised your concerns to the relevant authorities. We seek your understanding and patience in this matter," TPG added.

Singtel refuted TPG's accusations in a post on its Facebook page a few hours later. It said testing of the porting system had been completed successfully and Singtel, StarHub and M1 had written collectively to TPG on Feb 10 to say that all three telcos would support mobile number porting when TPG launches its commercial service.

"To our knowledge, they have not launched their commercial service," Singtel said in its post. "TPG needs to give us sufficient notice of their launch so that we can implement the necessary front-line system changes and training to facilitate the service. Unfortunately, they have not responded to date."

TPG called a halt to the war of words an hour or so later when it said it would suspend its mobile number porting service "following industry discussion and coordination with incumbent mobile operators". It did not respond to queries from The Sunday Times on how many of its customers were affected.

The telco's commercial launch was widely expected in December but was delayed to some time this year while coverage and performance issues on the 4G network were ironed out.

An Infocomm Media Development Authority (IMDA) spokesman said in a statement yesterday that telcos have to complete all coordination work with other parties, including other telcos, before launching new services.

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"IMDA has required TPG to complete this process before offering mobile number porting to consumers," the spokesman said.

The IMDA has also asked the other telcos to quickly resolve porting requests from affected customers' while the coordination process is being completed, he added.

Singtel and TPG are also locking horns in their bids for at least one of four 5G licences up for grabs ahead of the impending rollout of nationwide 5G networks.

Both submitted a solo bid earlier this month, while StarHub and M1 submitted a joint bid.