>>>You can buy smart phones for 30$ in shenzhen electronic malls today.

1) That's in Shenzen. Might as well be Mars for most people. When Shenzen hardware is sourced by global brands, they usually have a generous markup where that "$30" quickly disappears.

2) How long do they last? "Oh, but they're cheap. If it breaks in 3 months, just buy another!" No. People just don't want to go through possibly losing data and having hardware just suddenly drop dead on them.

So, yeah. I'll go with the guy who said five years. That's for stuff that won't drop dead in three months.