Apparently for iOS specifically, there is no Bluetooth API exposed via the SDK. While the rest of this answer may apply to other platforms, you aren't going to be able to make it work in the iPhone.
For other platforms... as far as I know there's is no API for Bluetooth access in Flex. You have a few other options though:
- This document describes how to use a third party tool or library to interact with Bluetooth (specifically to interact with a Wii remote, but you could presumably extend that to more general purpose applications).
- AIR supports native extensions, which you may be able to use to access the native Bluetooth functionality on each device.
Both options may require you to handle the cross-platform nature of the problem yourself, however (unless you use a third-party Bluetooth API that is itself cross platform).
You may also want to check out this blog post, which goes in to some detail about how a user achieved a similar thing to what you may be asking for.