iPhone and data security

Recently, a client wrote asking the following:

Can someone access my iPhone's address book data through Bluetooth?  For example, if I have a sensitive ID number listed in a contact, can someone steal it off the phone?

Our reply:

You'd have to jailbreak and hack your own iPhone first to allow it to use BlueTooth technology for data transferring. It's defaulted by Apple to explicitly use BT for devices only (headsets, printers, keyboards). 

However, your data is susceptible to relatively easy theft when using public WiFi (cafes, libraries, etc). The big online banking apps, websites, Gmail and the like use secure protocols (you can tell by the https:// as opposed to http://) to prevent this.

If you keep sensitive information in your iPhone's Address Book, you should at least passcode lock your iPhone and enable Mobile Me's (free) Find My iPhone service, so you can remotely send messages, GPS locate, or brick (lock and/or erase it) in the event of loss/theft.