Millions of O2 customers have been unable to to make or receive calls or data since around Midday today.
The mobile phone company says it has now fixed the fault but that customers may still experience problems as full service returns.
More top news
Even if you're having a tough day in the office, it's unlikely to be as difficult as the one facing the director of the US Secret Service.
The first behind-the-scenes photographs of George Clooney and Amal Alamuddin's Venice wedding have been published in a celebrity magazine.
The US Secret Service chief faces questions from politicians today over the latest in a series of worrying White House security breaches.