The O2 phone network has been hit by outages across the UK.
Customers have complained that they cannot access data, make phone calls or send messages.
Users in Edinburgh, Glasgow, Aberdeen and Dundee have reported issues with their mobile reception.
O2 has asked customers to “reboot your phone to help clear the issue”.
Monitoring site Down Detector reports other providers which use O2’s network, such as GiffGaff, have also been affected.
Football pundit and former Manchester United player Gary Neville has complained to the company.
“Hey @O2 your network is down in Old Trafford,” he wrote on Twitter. “Not a surprise normally but it’s not match day!”
An O2 spokesman said: “Some customers may have experienced an issue when using their mobile earlier today. This was fixed within 40 minutes. Some customers may continue to experience some intermittent issues when reconnecting to the network. We’re investigating what happened and apologise for any inconvenience this may have caused.”