Deactivate new phone to go back to using old one
I got a galaxy s5 active back in late August of last year on a 2 year contract, but I'm at my breaking point of missing apple/imessage etc. In an ideal world I'd buy an iphone 6, but since the etf would make that a bit out of my price range (note: not interested in at&t next) I'm considering simply reverting back to my iPhone 5 which is in good shape.
So my question is, can I make my iphone 5 my phone again, and deactivate the s5? And if I do, would the option of using my s5 still exist if my iphone 5 stops working down the road before my contract is up in August of 2016? Thx