Since fragility is mentioned, I'll have to chime in:
While the 7100 is better in many ways ("phone" like form factor), ruggedizedness would not be one of them from what I have heard. Although it's not too bad compared to other phones such as Treo's (Treo's are more fragile), there are stronger BlackBerries available.
For a stronger BlackBerry, I recommend the full QWERTY models. Some people have accidentally dropped 72XX series from 9 feet high down to concrete down stairwells and garages, and the BlackBerries survived. The 72XX series are among the most ruggedized phones available and almost never need to be replaced.
From this thread, it is clear that certain models survive abuse much better: BlackBerry Abuse Thread: Amazing Survival Feats