Thousands of O2 and Tesco Mobile customers across the UK experienced mobile signal blackouts for seven hours on bank holiday Monday following a network outage.
Although Tesco Mobile is a separate company from O2, the mobile operator runs a virtual network that piggy backs off O2's infrastructure, so O2's problems instantly affected it too.
The outage affected O2's network across the country, from Glasgow in Scotland, to Liverpool, Manchester and Birmingham, and even down to London throughout the afternoon and night on 25 May.
Users began complaining about the service dropout in the late afternoon on social media, and numerous users said that O2 customer support told them to reboot their phones, but wouldn't admit to an outage.
It was only at 8:22pm that an O2 spokesperson responded to complaints on the company's Twitter account, followed by Tesco Mobile at 9.16pm.
Even Sajid Javid, the UK government's secretary of sate for business, innovation and skills, was annoyed enough to tweet about the issue, asking O2 to "sort it out".
An O2 spokesperson told IBTimes UK that the problems with its network have now been resolved and a full service is now running: "Yesterday some customers experienced a problem accessing our network and we apologise for the inconvenience caused to those customers affected.
"Service returned to normal at 23.35 hrs. We will now begin a full investigation to identify and understand the cause."
Some users have been tweeting O2 asking whether they will receive compensation, and there are Twitter users who were complaining about having no service at 1am BST on 26 May.
O2 says that in this case, no blanket compensation will be offered to its customers, but the mobile operator will consider compensation on a case by case basis.