Some iPhone users on the O2 network have been unable to access the internet on their phones over the weekend and during Monday because of a problem with data access.
The problem left users unable to download any data from the internet or access any internet-based services.
O2 has acknowledged the problems on its Twitter account, saying the service would be back up and running on Sunday night. But despite a brief respite on Monday morning, there were still problems today.
The O2 Twitter account said on Sunday, "We're sorry that some mobile customers have had problems with data today - these services will be back up tonight."
A spokesperson for the company said engineers are working on the issue. "We are aware of an issue currently impacting data access for some of our customers. We are working to resolve this as quickly as possible and apologise to any affected customers."