I've programmed on a single hand held device for extensive periods of time, my TI-83. Sure it was a pain to always been putting it into Alpha-lock to use the letters, and it's keyboard wasn't in any kind of layout like QUERTY, but having access to all the buttons on the TI made actual programming possible. Maybe the TI-91/92 would be even better.

Right now my phone is auto correcting code to coffee.