Just about to give notice to close my O2 contract at 11 months, and will
then seek out and take up another cashback deal.  Looking around
tentatively, it seems quite likely I'll want to go for another O2 one in
fact, which makes life a bit more interesting as regards keeping my number.

I've read various reports on this ng of how to do this, using a PAYG
service as an intermediary.  What I was considering doing was as follows:

1. Give notice to O2 and ask for PAC code today
2. In 2-3 weeks, open a new O2 contract which will run alongside the
first one (I don't care - it will be free anyway!) with a new number
3. PAC out to an existing Vodafone PAYG sim card (already up and running
in my name, last used months ago)
4.  After a couple more weeks, after the original O2 contract has
closed, PAC from Vodafone to the new O2 contract.

Will that work, in that the new O2 contract will have been up and
running for 2-3 weeks on a new number?  Or can you only PAC in when you
are setting the account up? The idea of doing it that way is that the
two O2 contracts will overlap and I can avoid having to dial out on PAYG
for a couple of weeks (any incoming calls will go to the Vodafone SIM,
in a spare phone).

(By the way has anyone ever heard of cashback deals being invalidated by
changing the number after the contract has already started?!)

Thanks
David