Help needed with Multisave for non-O2 number switching to O2

[GliderPilot730]

I want to add my son to my account, he does not have an O2 number but wants to switch. If I order the phone that he wants on my account, when he receives it can he send O2 the PAC number then add the number to a multisave plan?

Secondly, he also wants an apple watch. In the basket it says "All smartwatches in the basket will be linked to your connection" Does this mean it will be linked to the phone purchased at the same time or will it be linked to my current number?

[MI5 · Accepted solution]

@GliderPilot730 

How to port in his number here Guide: Migration & porting into O2  

Discount details here Guide: O2 Open & Friends and Family discounts - How to sign up 

It should confirm the number the watch will be linked to in the summary, which can only be a new temporary number at present as his number won't be ported in.