Why it won't be easy for a new telco to enter the scene

It would need a domestic roaming agreement.

For the three telco aspirants, locking horns with each other is but the first hurdle they have to overcome as the lack of domestic roaming agreement poses a bigger challenge.

According to the latest report by DBS Research, the absence of domestic roaming may push the new entrant to cover the entire island from scratch.

DBS cited U Mobile in Malaysia as an example. U Mobile had a 2G domestic roaming agreement with Celcom to provide nationwide coverage, while it focused on rolling out its own 3G network, mainly in key urban cities.

"U Mobile in Malaysia managed to capture just 5% revenue share in 2014, almost seven years after its launch as there was no mandatory domestic roaming in Malaysia," DBS stated.

It noted that U Mobile did sign roaming agreements with other operators it probably had to pay a steep fee.

"While Singapore's small size is a big advantage in rolling out the network, the absence of a domestic roaming agreement is a big obstacle. However, one cannot completely rule out a roaming deal being signed once the new player secures the spectrum," the report said.

Still, DBS sees it possible for the new entrant can still possibly sign a roaming agreement with one of the existing players.