In September 2017, TalkTalk confirmed that it was looking to exit mobile, in an attempt to cut costs and renew its focus on cheap broadband packages. One of the options at the time was a "low touch" arrangement with a big-name mobile operator that would enable it to offer customers mobile service without having to do any of the heavy lifting.

Customers can choose to break free from TalkTalk and ignore O2. However, TalkTalk is incentivising customers with up to 25 percent off certain O2 tariffs. The deals aren't just available to existing mobile subscribers, they're extended to broadband customers too.

"As part of TalkTalk's simplification, we're changing how we offer mobile services. This agreement with O2 gives TalkTalk customers access to a wider range of great value 4G services," said TalkTalk in a statement. "It's great news for customers and allows TalkTalk to continue investing in our fixed network, delivering even better landline, broadband and TV services."