I have finally worn out the Samsung phone I bought over 4 years ago. It has served me in North America and New Zealand on both month-to-month and, currently, prepaid plans. It is unusual for people to "wear out" cell phones before upgrading, but generally all I want in a cell phone is lightness, call quality, and durability. Although the iPhone calls to me, I'll live for now with my iPod Touch and prepaid, saving the $80+/month.
As a replacement, I just ordered this. It's light, simple, supposedly has great call quality, and the reports of its durability are fantastic. Apparently it was intended for emerging markets but failed to catch on.
 It has a crack through the case and shuts itself off in my pocket, or now during calls.