I'm already a BT customer, but out of contract.
I’m a few days away from the bill coming from BT.
I am thinking about taking one of the BT offers, But I don’t what to end up pay two times…If I sign up with one of the BT offers.
If I sign up with one of the BT offers now would I require to pay the coming bill of the old BT contract, or would there be no upfront costs If I sign up with one of the BT offers.
You are not actually out of contract, you are on a rolling contract and still a customer hence deals for new customers won't be available to you.
If you are considering an offer shown on your MyBT, you will simply recontract under the terms of the new contract.
You won't have to pay twice if you recontract. Your pending bill will probably go through under your existing terms then the first bill under the new terms will include an appropriate adjustment.