Some Sky Mobile and Giffgaff users have reported being unable to make or receive calls and texts on Friday.
A Sky Mobile spokesperson said it was working to get the problems resolved “as soon as possible”.
Giffgaff confirmed issues had been reported by customers since “late morning”, affecting calls and texts.
“Our technical teams are still working hard to restore these services fully,” a Giffgaff spokesperson told the BBC.
Downdetector had around a thousand reports apiece of problems with Sky and Giffgaff on Friday. Users self-report technical issues to the website.
Both networks rely on O2’s mobile network, as does Virgin Mobile – which recently began moving customers to O2 networks after the two operators merged in 2021.
Tesco Mobile also uses O2’s network.
O2 customer support told Twitter users flagging issues with its network that “technical teams are aware and are working to fix this as quickly as possible”.
Although Sky Mobile’s data services continue to work, the mobile phone disruption comes on a Friday when many customers will be making weekend plans.
One Twitter user, Leslie Jones, wrote: “O2. We are without a signal for more than 24 hours. Unable to make or receive calls. Please advise what you will do to fix this, urgently , as we have a 97-year-old mother.”
