With mobile service disruptions the bane of working adults here, some users have called for operators to help one another out when there are outages, such as the five-hour one suffered by M1 users just last month.
The Infocomm Development Authority (IDA) - the telecoms regulator - has said it is studying this arrangement, which will require telcos here to form a "national roaming" network.
But it highlighted the steep costs involved, with analysts and operators agreeing that such a system will be hard to pull off.
A Straits Times reader, Mr Yeo Wee Lee, had suggested in a letter to the Forum pages last year that telcos here provide national roaming services. "This could be useful when one telco's network suffers a major disruption such as the (January 2013) M1 glitch. Its subscribers can then use the other telcos' networks."
Reader Jeremy Aw also suggested national roaming last month after M1's five-hour outage in the same month. IDA has since come out to outline the challenges involved.
This could mean "substantial investment by the mobile operators to significantly expand their network capacities", the IDA said in a letter in the Forum pages last month. "The complexity and costliness of such an option have to be carefully considered alongside the potential benefits," the authority said.
Telco players and experts also told The Straits Times it may not be commercially feasible to have national roaming.
While it is difficult to estimate the costs of expanding a telco's network, SingTel said last April that it spent $150 million over the past year to complete its nationwide rollout of its 4G network.
One of the few countries which will have national roaming during any disruption is the Netherlands. It rolled this out after a 2012 outage of operator Vodafone's mobile services affecting about a quarter of its five million customers for days.
Mr Michael Stephens, vice-president of global services for the Asia-Pacific region at United States-based telecoms equipment maker Coriant-Tellabs, said there were commercial issues if a telco's mobile customers, who paid less for their services, could get access to more premium services offered by another operator under national roaming.
"This undermines the latter's investment decisions and it creates an unlevel playing field," he said. It might make more sense for the telcos to plan other back-ups, such as rolling back upgrades that caused the network outage, he added.
Ms Serene Chan, a senior industry analyst of infocomm technology practice at market research firm Frost & Sullivan Asia Pacific, said the extra network infrastructure may be underused when there are no disruptions.
When contacted, SingTel, StarHub and M1 said they had discussed national roaming with the IDA and pointed out the technical challenges.
These include the risk of national roaming worsening the outage and causing overloading of other telcos' networks. At the end of last year, M1 had 2.1 million post-paid and prepaid customers, StarHub had 2.35 million and SingTel 3.96 million.
In response to The Straits Times' queries, IDA said it will weigh factors such as the extent of the roaming area, the types of services to be covered and quality of service issues in considering the implementation of national roaming.
Other factors include the infrastructure, the impact on competition and the incentives for each operator to ensure resilience in its own network. IDA said the issues are "complex" and it is "still studying various options".