Why they charge more for cash....
It's all to do with box breaking, where a phone is bought to be sold on abroad. Obviously these phones are subsidised by the carriers/dealers, and to recoup their money they need them to be topped-up and used. They seem to have found most box-breakers are none to keen to hand over their plastic.
On another note, the articles claims the Nokia 2330 Classic and 2220 Slide are the same, they are not. The 2220 doesn't have bluetooth!