Is my logic flawed?

10_to_3

Hi,

My contract is coming to an end soon and I intend signing up for another cashback deal. I want xnet minutes and texts but at minumum cost, preferably free, and with one of the more reputable cashback companies. I am happy with my current phone and am willing to get a rubbish phone on the new contract in order to get the best value minutes and texts.

Will there be any trouble doing the following:

Transfer existing number to new sim card.
Get both old and new phones unlocked.
Transfer new sim card to old phone.
Stick pay as you go sim into new phone.

Then I'll have decent deal and a phone I like. Any flaws in my logic?

Thanks.