About 10% of the company's 23 million customers were affected for three hours
UK's mobile phones and broadband provider O2 has apologised for a service outage which hit millions of its customers on 12 October 2012.
The company said that due to technical fault about 10% of its 23 million customers were affected for three hours and the network has since been restored.
O2 is not offering any compensation for customers affected by the outage which is second such incident in three months for the UK's second-largest mobile operator.
An O2 spokesperson said: "One of our network nodes, which help connect and manage traffic, experienced a partial failure on Friday morning.
"By lunchtime this caused a number of our customers to have difficulty connecting to our network to make calls or use data," spokesperson said.
"A fix was found by 3.30pm and service was restored by late evening on Friday."
"A small number of customers have experienced a further delay as the backlog of network requests clears," spokesperson added.
The latest outage is the second outage for O2 as in July this year the company's first outage saw its mobile customers stranded without any network service for the best part of 24 hours.