How long are windows phone built to last?

They last really really long Samsung Omnia
WP 7.5:

Never used any screen guard:

Or any cover:

Still running like charm. No lagging.

All hardware buttons are same.

Dropped it like 8-9 times,  not even a single visible dent.

But you know what, stopped using it recently. Reason? Got bored. 

They are good, no doubt.