O2 - which is the second-largest mobile network in the country behind EE - issued a statement saying: "We are aware our customers are unable to use data this morning".
Some users are still reporting issues with voice calls.
The company is blaming software issues at one of its suppliers for the problems. O2 says technical teams are working "extremely hard to resolve this".
"We'd encourage our customers to use Wifi wherever they can and we apologise for the inconvenience caused".
MOBILE phone users across the Isle of Wight are facing network problems this morning, as 4G and data services on O2 have stopped working.
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The network also provides services to Sky, Tesco, Giffgaff and Lycamobile networks. Londoners, for example, are finding that the Countdown timers at bus stops are all crippled as they can't communicate with London's transport executive, TfL.
The Telegraph confirmed that some customers of these other networks were also affected by the outage.
Some customers have reported being unable to use their data, while others are struggling to send texts.
Thousands of O2 mobile phone users have been left unable to access the internet because of a technical fault.
"Our technical teams are working with their teams to ensure this is fixed as quickly as possible".
It is not clear when the issue will be resolved, but O2 said it would share further updates as soon as possible.
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