Three mobile customers say they are still unable to make or receive calls this morning.
More than 9,300 issues were reported on the outage detection site DownDetector yesterday.
Customers asked what was going on, with some saying this was not the first time they had experienced problems.
While issues appeared to be resolved overnight, the number of outages recorded on DownDetector crept up this morning to 614.
Posting on DownDetector, James Foreman said: ‘In Buckinghamshire and the service is still completely down. No calls or internet. This is a joke.’
Rob Edmunds added: ‘Been down all day here in Norfolk, I need my phone as a heart attack patient and diabetic and I cannot call my doctors or 999.
‘I have tried resetting, restarting, switching SIM to old phone but nothing at all. No landline and unable to use WiFi calling.’
Mitchell Anthony added: ‘Day two of not being able to make or receive calls!’
People reported concerns this morning in areas including Cornwall, Gateshead and Lincolnshire.
Three said it is investigating the cause of the blackout.
In a network update, Three said: ‘Following an issue earlier today [Wednesday], voice and SMS services are now returning to near-normal levels. Data services continue to work normally and we are monitoring the network closely.
‘We understand how disruptive this has been for our customers and sincerely apologise for today’s inconvenience.’
It comes after users reported problems at Three in January this year, with some again saying they were unable even to call 999.
A spokesperson said at the time: ‘We are aware of a number of reports that customers have not been able to connect to 999 calls. Data from the emergency services shows that normal volumes of 999 calls being placed via our network are being connected.
‘We are taking these reports very seriously and are investigating this urgently, and we apologise if anyone has been unable to successfully contact emergency services.
‘While it is likely your call will connect correctly to 999, if you have any issues, please try another network or landline. Please do not try and test 999 calls from your device as it may prevent genuine calls being answered quickly.’
Three has been approached for comment.
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