Each iPhone contains a unique Exclusive Chip Identification (ECID) number that identifies the phone to the cell tower. With access to the BBP via jailbreaking, hackers may be able to change the ECID, which in turn can enable phone calls to be made anonymously (this would be desirable to drug dealers, for example) or charges for the calls to be avoided.
The filing also goes on and on about how evil jailbreaking is. Pure propaganda if you want my opinion.
Come on Apple, with all the money you spend on these legal fees, you could at least make the effort of finding good reasons for not jailbreaking. On my end, I do have as much as 30 reasons to jailbreak 😉
Next thing you know, Apple will tell you that every time you jailbreak an iPhone, a puppy dies somewhere.
Via Slight Paranoia