I’ve been given an iphone from a mate which is locked to 02. I read that it can be unlocked for free, but does her sim need to be in the phone for this to happen? Shes currently using a different handset…

I assume so, but thought I’d ask!

Yes it needs a SIM in the handset to finalise the unlocking process, the SIM has to be a different network.
Pretty straightforward process, I’ve done it with three different iPhones so far.

Might’ve been prudent to get the friend to unlock it, can you give it back to them temporarily so they can call O2?

O2 iPhones can be unlocked online by the owner.

Give the phone to her and she can do it for you.

As long as it is not a 6.

I don’t think O2 are letting those be unlocked yet.

does her old sim need to be in it, or can does it work if my sim is in there?