A power-related issue was behind a disruption to Singtel's mobile services that affected many users islandwide for more than three hours from around 10pm on Thursday.
The Straits Times understands that it was an internal power issue.
Apologising for the service disruption, the telco said in an update on Facebook at 1.20am yesterday that it detected issues with mobile voice and data services on its 3G and 4G network at 10.11pm.
"Initial investigations indicate that this was due to a power-related issue. Affected services have been progressively restored from 11.50pm and we will continue to monitor the network closely to ensure full restoration," said Singtel.
It will be offering its mobile pre-paid and post-paid customers a day of free local mobile data on Nov 10, a Saturday.
A spokesman for telco regulator Infocomm Media Development Authority said it is investigating the incident.
I could... not use the phone network. This caused me great inconvenience.
SINGTEL USER CHLOE POH, who was unable to call for a Grab car to get home after an office event.
While some customers said service was restored for them after Singtel's 1.20am update, others still had issues connecting to the Internet on their mobile lines.
The telco said later at 2am that as of 1.22am, all affected services had been restored.
A Singtel spokesman said yesterday: "We regret last evening's service interruption that affected mobile voice, SMS and data services...
"We apologise for the inconvenience caused to our customers and thank them for their patience."
On Thursday night, many Singtel mobile users said they were unable to make calls or access the Internet.
Customers took to Singtel's Facebook page to complain about service disruptions in areas such as Jurong, Bishan, Ang Mo Kio, Bukit Merah, Woodlands, Orchard, Sengkang and Potong Pasir.
Between 10pm, when users said they started experiencing problems, and about 11pm on Thursday, there were at least 200 posts complaining about the lack of calling, text messaging and 4G data services.
Singtel first posted about the disruption at about 11pm, noting that there were mobile network issues, and that its engineers were looking into the matter.
In an update at 12.20am yesterday, Singtel said: "We regret to inform that some customers may be experiencing intermittent difficulties accessing mobile voice and data services on the 3G/4G network."
By 1am, Singtel's post about the disruption had received about 2,000 comments, about 1,800 reactions - including likes and angry reactions - and 770 shares.
In a Facebook post before Singtel's update, user Jess Woo said she had tried to restart her phone multiple times in the last hour.
"Till now no response or official updates from Singtel on their page," she added.
User Chloe Poh said she tried to call for a Grab car home after an office event but could not do so. "I could... not use the phone network. This caused me great inconvenience. Please give an explanation."
Legal trainee Tan Anqi Angelina, 24, told The Straits Times that she relied on her home's Wi-Fi network to surf the Internet.
"I'm not exactly sure when service resumed but when I went to bed at around 1am, it was still down," she said.
Another Singtel subscriber, Ms Lim Lee Ren, 25, said she was not badly affected, as she was at home and could still rely on Wi-Fi.
But Ms Lim, who is an analyst at a finance start-up, added: "It would have been problematic if I was out and unable to reply to my bosses who need replies 24/7."
• Additional reporting by Timothy Goh