Vintage Paw, can't you just turn up to an o2 store on the 24th June and get the whole lot, or are you not with o2 currently? That's what I was going to do.
I am with them, yes.
Actually, as usually happens, after posting daft questions on teh internets, I've actually phoned them and asked
I've already ordered the phone from Apple, so no worries about the shop having stock or not. It won't arrive until 14/15th July though. (I want a Simplicity tariff, and, despite what I posted previously, the O2 shop dude told me I wouldn't be able to buy the handset from them on Thursday for use with a Simplicity tariff because it's essentially a payg handset, which they are, indeed, not doing yet.)
In the meantime, I'm going into the O2 shop tomorrow, with my order confirmation from Apple, and they will give me a new micro-sim that I can pop in my current iPhone and activate. Then, on 8th July when my current contract runs out, I can call O2, who will switch me to the Simplicity tariff I want. I'll keep my number, keep that new micro-sim, etc. Then, when the new phone arrives, I just pop out the micro- bit of the new sim, and pop it in the new phone, and it carries on as normal.
The only thing complicating it was the change in contract half way through the process. I haven't swapped a sim before without having a whole new contract, so I wasn't sure how it worked.