The BB424 works with the IP485G phone. The programmable buttons allow you to press one button for operations that would normally require pressing several buttons. For example, you could configure a button to speed-dial a particular extension or external number. A different button could be programmed for silent coach, and so on. The icons displayed for a programmed button show you the status of the target extension, which is especially useful for features such as monitored extensions or bridged call appearances.
Note: The ShoreTel BB424 and BB424 are identical key expansion modules, but have been rebranded since purchased ShoreTel in September 2017.