They've said several times on Twitter today that it will be available tomorrow. I even asked outright if I could go into a store tomorrow and walk away with one, and they said yes.
The unfortunate thing is that you get a different answer depending on who you speak to in O2 (or anywhere for that matter) - it's either definitely in store tomorrow, or they don't know anything about it. It's a mess, really.
I guess the only way we will know for definite is by waiting for tomorrow. I'm not confident enough to go waiting outside a store in the morning, that's for sure. In fact if I can order it on-line for delivery Friday, I'll do that - if only so I don't have to wander around shops getting blank stares from anyone I ask about it ;)