I'll agree with the others about the longevity of a Blackberry, and add:
I've had a number of cell phones over the past 16 years, and several blackberry's over the past few, including: 8700, 8800, 8100, 8300 and now an 8900 on T-Mobile. None of these ever failed, and the most maintenance any required entailed replacing the battery or upgrading the firmware - period.
Treated nicely, there's no reason for these devices to "fail". I have a couple of old 8700's that still work perfectly, and I'll swap my SIM into one of these temporarily for "rough duty" (e.g., if I'm out in wet weather, etc). Still work like new. About the only thing I can see going "bad" on one of these might be the keypad or trackball -- and these can be easily replaced for a few dollars down the road if need be.
I had used my 8300 quite heavily for about two and a half years, and only sold it when I upgraded to an 8900, even though the 8300 was still working like new.
Take good care of these, and they'll generally last for years.