I'll buy/sell phones about every 2-3 months. I usually get one "brand new" flagship phone per year, usually on-contract, the rest are off of swappa (I try to wait until last year's model is under $300, then do the buy-sell game to cheaply try out different devices). Sometimes I go back to a phone I used to own if I get nostalgic. Still haven't found a perfect phone yet. I guess I'd want an unlockable bootloader 2013 Moto X with the 2014 X's internals, with the Note 3's (or Note 4's) camera.
It's my only hobby
In the past 12 months...
Nexus 5 (two or three times)
Note 2
Note 3 (twice)
Moto X 2013 (twice)
Moto X 2014 (pure edition on AT&T and 2 different moto-maker versions on verizon)
Droid Turbo
Oops...I guess that's 12 phones in the past year.
My wife could care less about what phone she has (other than it has to be BIG and have a pen...so a Note). So I also get my fix upgrading her phone. She's had the Note 2, 3, and 4 in the past year.