Buy the phone of your choice unlocked and outright.

Then get a SIM only deal for £15-£20.
After two years you will break even.

At the end of the two years, sell the phone on Gumtree for (say) £200, and use the cash towards your next phone.

Overall, you'll be spending roughly £20-£30 a month instead of £45.

I am the same as you and on EE and have been with them/orange for many many years now and I wanted the S7
also but refused to pay £45 a month. So I rang them and asked for my puk code as I wanted to leave and get a cheaper deal elsewhere. They rang me back and asked why I was leaving and I told them I was not going to pay the very high price they were asking and it would be cheaper with Carphone Warehouse. The guy said he would look to see what he could do for me. I ended up with the a gold Galaxy S7 for £32.50 a month as EE do not want to lose their loyal customers. I am happy with that and received my new phone the following morning. Job done!

Supported Palace for over 69 years since the age of 7 and have seen all the ups and downs and will probably see many more ups and downs before I go up to the big football club in the sky.