O2 customers in parts of London, Kent and Sussex have been unable to make calls, access the web or text today after the network went down.
The outage was first reported late Monday night and at time of writing was still ongoing. The network blamed the lack of service on a "theft and vandalism at one of our operations sites in East London".
"As a result, customers in East London, North London, Kent and Sussex may be experiencing problems making or receiving calls, texts or data," the mobile network said in a blog.
The network said it was an organised crime that deliberately targeted the operations at the site. Engineers are currently on site working to replace the stolen equipment and repair the vandalism but we were unable to give a time when the network would be back up, although O2 hopes that it will be today.
"We have extensive continuity plans which we are bringing into effect now. The nature of this theft has prevented us from restoring service immediately but we expect to do so today."