One more thing: sometimes attachment handlers are unable to respond to attachments in email messages that arrived before the attachment handler was registered. I say "sometimes" because the behavior is somewhat inconsistent (i.e., I used to notice this behavior consistently on OS 4.1 and earlier devices, but I have some tests which have shown that this is not necessarily true on 4.2 or later devices).
Karl G. Kowalski
Owns a RAZR
Develops for BlackBerry
So next phone will be........an iPhone 3G!