Dust-off the archives
Nokia could be the "come back kid" so easily, and without spending a penny on development:
3310 and 6310i.
There is NOTHING on the market to rival the simplicity and build quality of these handsets, therefore completely ignoring the needs of those who do not want a smartphone, but similarly do not want the buggy, flimsy & cheap crap which is the only non-smartphone option available now.
Businesses would order 6310i s by the bucket-load, and I reckon the 3310 would fly too.
Biting the hand that feeds IT
