Why Don’t Mobile Phones Last The Contract Length?

I think I got my first contract mobile phone when I was about 20 or so. Back then, I think I was with Three and I had this really cute white and green phone that I now can’t remember the make of. Anyway, I loved it but when my 12 month contract ran out, I was glad that I could pick something else. Over the years, contracts have slowly changed from 12 months, to having an 18 month option to only being 24 months in length. I remember the first time I had to have a 2 year contract and