Will a EE SIM card work in an iPhone 5s that is locked to orange?

I've just bought an iPhone 5s, about to put in an orange pay as you go sim and I'd like to know if I can switch to EE without having to pay to have the phone unlocked?

If you have an orange SIM card you are already with EE as they are orange merged with t-mobile so there's no reason it won't work!

Orange, t mobile and orange sims can be used in any of their phones. I've got a orange ipad with an ee sim in it, and my mums t mobile sim works in my orange phone