I am looking to purchase an Apple Watch and add it to my existing contract, but gift the watch to my partner so she can use it. She is on o2 as well. Is this possible or will the watch be linked and using my mobile number?
It will be linked to your account unless you pay it off in full to release it.
You are better advised to buy from Apple directly.
You can still pay them in installments.
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion. This is not Customer Service so we are unable to help with account specific issues.