1 - Be sure you have the BlueChat installed in two mobiles and have Bluetooth turned on in both of them.
2 - First of all, you need a server. Start the application in a mobile and press "Run RFCOMM server" in the main menu (it will use RFCOMM communication protocol). Accept the connection request that the mobile will ask. After that, you will see a wait screen with the text "Waiting for connections".
3 - Now, you need a client to be connected into the server. Start the application in the other mobile and press "Start RFCOMM client" in the main menu. The mobile will inquiry for all the Bluetooth enabled devices in the current area, it could take some minutes, just wait... After that, it will display all the devices found in a list (it will show the Bluetooth device name when it is possible or in, a second choice, the address), select the device that you want to connect in the list an press the "Selec" button. You need to accept the connection request that the mobile will ask. Automatically, it will connect to the first service running on the selected device. If the device you are trying to connect does not contains the Chat service, you will get an error, so be sure it is the right one.
4 - If all these steps worked until now, you will be connected. Then you can exchange messages between devices just writing in the field and pressing "Send button".
PS 1: If you got any weird problems during the client connection, you might have to restart the application.
PS 2: If you want to connect another client, just repeat the step 3. The application supports more connections, but some mobiles can not. In the emulator, it works fine.