Daughter has a new phone, on EE. Not bought by me. I mentioned to sales person that I wanted to pop in her previous/current O2 sim so she could download priority app. She doesn't use the app much, but it's nice for her to have it there. Salesperson told me if I did that it would lock the phone. I'm not paying the contract, so didn't want to go ahead and try it anyway. Is that actually true? And if so, any recommendations for a cheap phone she could use to download the app onto?