If you're missing calls and texts at a particular location or data speeds are slow, it's possible there's an issue with signal strength.

Check the current status of the network at your postcode, here: https://status.o2.co.uk/

If no faults are showing on the network and / or the problem occurs at more than one location, outdoors, there might be a fault with your phone itself or your SIM card. Here's how to check: 

• Does anyone else in the same location on the O2 network have the same problem? if they do, there's a signal issue.
• If you're indoors, check your signal strength outdoors. Indoor signal can be affected by the building, trees and even the weather.
• Switch your phone off and on and after switching off, remove and reinsert your SIM.
• Still no improvement? Try your SIM card in an unlocked phone or the phone of another plan.com user. If signal reception improves, your handset could be defective. Contact your supplier.