Yes, but not at the moment @Grh142
o2 are moving to a new customer platform called 360, and while this is going on you cannot merge accounts to show more than one number in one login. Details about this are below.
https://community.o2.co.uk/t5/Welcome-News/O2-System-Updates-360/m-p/1598402#M39424
If you mean can you get a second number, then yes. It would be wise to do this in store to make sure it goes through as a new line and not an upgrade, plus you would get it going straight away.
You can do it online, but make sure you keep checking it is a new deal and not an upgrade.
Please note, this is not customer services and we cannot access your account. Do not publish personal details (email, phone number, bank account).
Link to our guide on how to contact them can be found here
