Virgin Media O2 has become the latest telecoms giant to axe its ageing 3G network - a move that could leave thousands of customers without mobile internet unless they urgently upgrade their devices.

The switch-off begins this month, with the city of Durham the first to feel the impact. Other areas will follow in the coming weeks.

While the network insists the move will improve speeds and reliability by focusing on 4G and 5G, customers still using older handsets face a grim reality: no data, no browsing - and not even a basic WhatsApp message will get through.

"You'll struggle to do even the basics," warned consumer finance site MoneySavingExpert, founded by Martin Lewis.

"Calls and texts over 2G may still work, but the quality will likely be far worse than you're used to."

Virgin Media O2 says most of its customers already use 4G or 5G devices. But for those who don't - including some of the most vulnerable - the clock is ticking.

Affected customers include users of Giffgaff, Sky Mobile, and Tesco Mobile, which all piggyback off the Virgin Media O2 network.

Jeanie York, the firm's Chief Technology Officer, called the change an "important milestone," adding: "We're putting support in place for anyone who might be impacted - especially those who are vulnerable or unaware their device is out of date."

The company is contacting customers directly, but with the switchover already under way, time is running out.

Check Now: Will Your Phone Still Work?

If your phone or SIM doesn't support 4G or WiFi calling, it may soon be obsolete for anything beyond basic calls and texts. V

irgin Media O2 has published a list of affected devices - and if yours is on it, you'll need to upgrade before the 3G switch-off hits your area.

For a complete list and advice on what to do next, visit the Virgin Media O2 website .