O2 customers will get up to two days' credit in compensation after a data outage affected millions of people.
The UK's second largest mobile operator, which has more than 25 million customers, saw disruption to its network begin at around 5am on Thursday and last for most of the day.
The firm said 3G was fully restored by 9:30pm on Thursday, with 4G services back up at 3.30am on Friday.
:: Pay monthly customers, SMB business and mobile broadband customers will be credited with two days of charges by the end of January
:: Pay as you go customers will get a 10% credit when topping up in the new year – O2 will notify customers when it is available
:: Pay as you go mobile broadband customers will get a 10% discount on a bolt-on purchase in the new year – O2 will notify customers when it is available
An O2 spokesman said: "We're very sorry about yesterday's data issue. We understand how important it is to stay connected, especially at this time of year.
"We'd once again like to thank our customers for their patience. We're doing all we can to make sure this issue doesn't happen again."
Four other mobile operators – Sky Mobile, Tesco Mobile, Lyca Mobile and GiffGaff – were also affected as they use O2's infrastructure.
They are each providing their customers with compensation, which will not include the O2 credit.
Sky Mobile customers will get a day's worth of free unlimited UK data on Saturday.
"We're really sorry for the issues you experienced on Sky Mobile yesterday," a Sky spokesman said.
"We're giving you a day of free unlimited UK data this Saturday 8 December, so you can catch up on all the things you've missed. You don't need to do a thing."
GiffGaff is setting aside a "goodwill fund" so any customers who felt the data outage "had a significant impact" can register for their share of the fund.
Users will be able to choose whether to take a share of the fund as credit, or donate their share to charity.
More from UK
Emails will be sent to customers over the next few days and registration will stay open until the end of Friday 14 December.
GiffGaff's CEO, Ashley Schofield, said: "I'd like to say sorry again that this has happened. We let you down and that's never something we want to do."