iPhone dev Raif Ackermann has managed to establish a working bluetooth connection between two iPhones. The connection uses two external bluetooth adapters that plug into the adapter ports and is based on the work by Matthias Ringwald for a user space bluetooth stack. The long-term goal of the project is to eventually get the connection working using the iPhone’s built-in Bluetooth support. There is even a possibility that the project may eventually be SDK-complient.
As the below picture shows, the method even works with iPod touches:
