I used a Nokia Lumia 900 for about a year and loved it. Technically a smartphone, but I got over a week of use out of a single charge! You might think the hardware is too slow for a smartphone OS, but this was the flagship WP7 phone - no lag or stutter. It also boots fast if you prefer to keep it off.
Note that AT&T will not allow you to activate this phone without a data plan. Just use a different provider.
Note that AT&T will not allow you to activate this phone without a data plan. Just use a different provider.