I'm using one (a Nokia flipphone). It's quite impressive considering its limited hardware. It has thetering, google maps, a browser, etc (the first 2 were hard requirements).

My demands were:

1. Long battery life 2. Small attack surface (security) 3. A phone that is so uncomfortable to use that I would use it only for calling, and some sms. 4. 4G network 5. Thetering 6. Google maps (the only thing that is really, really needed) 7. Flip phone (strong, no worryes about scratches, etc, and easy to put in a pocket).

It turns out to be the best decision I made in years .. no more distractions.