Iphone 4 locked to EE, options?

I have an IPhone 4 locked to EE and a contract with EE for a HTC one that I no longer have.

EE offers unlocking for 8.99, being that I'm on contract for a different phone does this mean i can't do it through this method?

another option would be to put in a PAYG sim into the phone and pay the 8.99 that way, my question is does that PAYG sim have to live in the phone for the whole 7 days or time it takes to unlock the phone? Or can it be switched out while the unlocking takes place.

You have to have the PAYG SIM in long enough for the phone ID and the SIM ID / Phone number to be linked on the service providers system, so they can verify you are using that phone.

Once the unlock request has been accepted, it should not matter.

You may need to talk to customer services and explain the situation. They are mostly helpful, but be careful when describing what you want - they often take a "locked" phone to mean password locked or locked out of the network; if they get that impression, they will stonewall you.

Tell them it's another phone that you are using on EE but you like to be able to use it on another network once your contract expires, rather than saying it's locked.

eg. O2 call it "Unlatching" not unlocking, even though it is a network lock…