How long do you have your current phone?

I own an iPhone 6 for a year and a half now. Before that, I owned iPhone 4 8GB model that I purchased in 2011. Prior to iPhone 4 I owned an Xperia Music.
So, as you can see, I don't buy new phones that often and I will keep iPhone 6 for the next 3 years at least.

Why iPhone? I am an iOS Developer. Apart from that, I don't care about customisation and I truly love the quality of iOS apps.