The answers range from 'not terribly useful' feature phone, to an iPod Touch with a bunch of options disabled (note: is not actually a PHONE), and wander into less secure territory from there.
"It's a security first-principles dilemma: the most secure device is likely to be the least useful to the average person."
Need a secure smartphone? Answer is simple, experts say | ZDNet
Making a good smartphone choice could be the difference between being hacked and keeping your data safe.