Wow, I'm surprised at how few TS readers seem to be enthusiastic about mobile devices. I love trying out new devices of all kinds, and I normally use my wife's or daughter's upgrade when it rolls around, since they have found a home with Apple devices. This puts me at roughly once every 12 months, I suppose. In rare cases, sooner. But I'm always reading and learning about new devices and I love to try out new tech.
If I could upgrade every 6 months, so long as manufacturers keep pace with compelling products [HTC One, Lumia 1020, HTC One mini], I would absolutely do so in a heartbeat. That's not to say that my mind is made up regarding these new services [always a skeptic with wireless carriers], but I definitely have enough interest to keep up with a plan like this.