I have a theory, phones are getting bigger and bigger which is a fact, just compare them to the Nokia 8210 and Motorola StarTac of yesteryear when the trend was for miniaturisation and incidentally two phones I owned.
However, since 1999 waistlines have been getting bigger and bigger, In fact the UK has an epidemic of obesity. While we are told that calling someone fat may cause them to suffer from body image anxiety the fact remains, fat is fat. People dying from starvation never look fat, it is all down to what you shovel in your mouth and the ratio of input and output.
So I reckon there must be a correlation between the FAT epidemic (bigger clothes, bigger pockets) and the increase in mobile phone size. In fact I even think that if a manufacturer came up with a phone that incorporated a snack compartment for sugary and high fat treats, they would have a winner. They might even consider extending the screen or keyboard for those with particularly fat digits.
A Fat Fone would be an instant hit.