Virgin Mobile says it has restored services to customers across the UK who had been struggling to make calls, send text messages and use mobile data.
Virgin Mobile said it would compensate customers for the problem which it said was due to a "technical issue".
Complaints began coming in on Tuesday morning in London, the Midlands, the North West, Bristol and Scotland.
Customers vented their fury on Twitter, with some complaining they had been left in the dark.
In a statement Virgin Mobile said: "We apologise for the disruption and inconvenience some of our Virgin Mobile customers have experienced today. This was due to a technical issue which we've now resolved.
"We will be compensating our customers for the loss of service and will let them know the details shortly."
It did not disclose the number of affected customers.
So no Virgin Mobile customers can make calls or send text messages, yet there is no communication from Virgin whatsoever. No status page, no Twitter acknowledgement, no replying to customer questions, nothing. Shoddy, #VirginOutage— Dicky Moore (@dickymoo) May 14, 2019
According to Downdetector, which tracks mentions of mobile outages on social media, complaints began en masse at around 11:00 BST on Tuesday.
It said most comments had been about mobile phone services, followed by mobile internet. A minority mentioned issues with their Virgin cable internet services.
One customer tweeted: "@virginmedia why are you posting trivial polls and ads on your site, but nothing about the mass outage on mobiles? Incredibly frustrating and very poor comms."
Another said: "I'm a full-time carer for my disabled mother. We're both on Virgin Mobile. You've crippled my day with this outage."
According to Ofcom, the level of satisfaction with mobile providers is generally high across the UK.
However, according to its most recent customer satisfaction survey, Virgin Mobile is the most complained about of the major telecoms companies.