EE and O2 have moved quickly to resolve technical problems that left customers unable to make calls to landline numbers.
The problems reportedly also affected networks including BT Mobile and Giffgaff and have since been blamed on a fault with the BT national network.
Angry users quickly took to social media to spread news of the incident, which ranged from an inability to receive calls to complete loss of signal.
@O2 hi is the network still down? As I still have intermittent signal and I've switched it off and on more times than I can count!— David T (@Davidtrem72) January 11, 2016
Anyone know if there's a problem with the O2 network in #Crewe - can't ring landlines from my O2 - and someone else has same problem— Belinda Ryan (@CreweChronBel) January 11, 2016
An EE spokesman said: "Customers of a number of operators experienced problems calling landlines for a short period.
"As you've probably already seen, this was resolved last night and wasn't just EE customers having issues calling landlines from their mobiles. We're working together with all the affected operators to investigate."
Meanwhile, O2 said that the main fault was with BT. The firm's live status page said: "We are aware of an issue where some O2 customers may be experiencing difficulties making calls from their mobile to EE mobiles and to landline numbers.
"BT, our fixed line partner, have confirmed they have started to see an improvement in call connections. We continue to work closely with them to monitor service and await confirmation that the issue has been fully resolved."
V3 contacted BT but had received no reply at the time of publication.
Giffgaff has also confirmed that the fault has been resolved. "On the evening of January 11th we experienced an issue where members were unable to make outgoing calls to landline numbers, 0800 numbers and some mobile numbers," a spokesperson said.
"If anyone is having trouble making calls this morning, the best thing to do at first is simply a reboot of your phone by holding down the power button to bring up the option to turn it off entirely, then turning it back on again. This will force a reconnection to the network."
It is not the first time major networks have faced downtime. O2 was criticised for a widespread network outage last year that left customers without service over a bank holiday weekend.
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