well, bfrye is making a good point. the wireless backups will capture any SMS and BWC messages that are currently on the handheld. that would be the only way they would be able to read those messages. even sniffing packets wouldn't help, as those packets are encrypted (and if they can break the encryption, then they should go work for the government).
just keep in mind that despite your having SMS and BWC emails, as long as you are on the corporate BES, any data sent to that handheld would technically be property of your company (not just the corporate emails). most privacy rules and whatnot in any typical united states corporation will state this.
In the beginning the Universe was created. This has made a lot of people very angry and is widely regarded as a bad move.