Instead of worrying about Jailbroken iPhones, perhaps Apple should be worrying about the security of the regular ol' non-jailbroken units based on this PC World item...

IPhone SMS Attack to Be Unleashed at Black Hat

They report that Charlie Miller, who first reported the SMS (text message) hack, now has a way to use this iPhone security hole to completely take over the with a series of specially crafted text messages.

Anecdotally, it seems to me that I receive a lot more SMS (text) SPAM on my iPhone's AT&T account than I do on my T-Mobile or Sprint accounts. This is a bit odd statistically since I've had my T-Mobile and Sprint accounts for many years longer than my AT&T account (signed up last November). So, it seems to me that my iPhone may be more at risk than my phones with other carriers.