Why is it a common scenario that all the Nokia N - series mobile hang?What makes a mobile hang?

It’s one of 2 things:
1— Bad hardware
2— Bad software

In Nokia’s case, it’s a combination of both, but their software is to blame more. Interestingly, though, cheap black&white Nokia phones are much much much better than the new Nokia “smart” phones in terms of stability, hardware reliability, and battery life.

Think about it: Why would a company make a crappy phone on purpose? If they made perfect phones, you wont be buying a new phone any time soon, right? Now apply that to almost every other company out there. See why so many things are just crappy? ;)