When you receive a message from another driver, it will start with the following sequence:
where [CODE] will be substituted with the code of the driver sending the message.
When you receive messages from another driver and you want to reply, you still must start the message with the nn + [CODE] sequence, as described here.
If you do not have the identification code of your colleagues, ask your fleet manager about it. Additionally, you can also find a quick guide concerning message sending here. You can print it and carry it around. Talk to your colleagues and fleet manager about it.
If you want to know more about driver to driver messaging and setting up driver identification code for messages, click here.