A German hacker group called Phenoelit - which I think is a spin-off from the Chaos Computer Club - reckons its found a flaw in BlackBerry's Enterprise Server software.
This is the software used by corporates to receive and push email about to company users of the BlackBerry PDA/phone from Research in Motion.
Basically the flaw appears to allow hackers to send specially formatted packets to the server and create a denial of service (DoS) situation.
From what yours truly can understand about the modus operandi of Phenoelit, the DoS attack only works if the sender of the DoS attack is inside the BlackBerry network of authorised users, or has post-firewall access to the server itself.
It's not serious, as Research in Motion says it is working on a patch, but the methodology used could be exploited in future attacks...