The feature you are talking about is commonly referred to as "Voicemail Drop".. This is not a built-in feature in 3CX, but I encourage you to take a look at our
3CX Auto Voicemail tool which does what you are looking for. Essentially your agents can pre-record standard voicemails with titles like "Sorry I missed you", or "Contact us", or "Your account is past due". Having the ability to select from a list of pre-recorded voicemails that, when selected, immediately drops the agent from the call and has 3CX save the voicemail in the background can significantly increase the productivity of your agents, and ensure a carefully crafted voicemail is left with your customers every time.