Two phones??

I am inexplicably fascinated by and addicted to The Verge's 'What's in Your Bag?' posts. I have also recently stumbled across a forum thread in which Verge readers show the world what they drag around every day. One thing that I notice looking at these is that many people seem to carry two smartphones. I am curious whether any reason for this exists besides 'one for work, one for play.' Any dual-wielders care to share?