Jayvee of Cellphone9 raises an interesting point:

"I choose a phone based on the knowledge that I know it will get stolen in two years."

And he concretizes this notion by not considering phones above $200 (about 30% over what a minimum wage earner makes in a month over here).

That figure may work for Jayvee, but not everyone is as responsible, or relatively well-off as he is. If you lose your smartphone or PDA phone every year, or if you swim in gold coins like Scrooge McDuck, then you'll have to go higher or lower.