We would like to see a "direct to voicemail" button. We used this feature extensively in IC, in the following scenarios:
Sales or other marketing/junk calls coming to the main number - the receptionist knows these people after a while and can tell the caller the person they are wanting to reach is unavailable and they could send the call directly to their voicemail without ringing their phone.
During a consult call, if the person doesn't want to talk to the caller at that time for whatever reason, the receptionist can go back to the caller and tell them they are unavailable and offer to put them in voicemail. With a button, they don't have to send the call back to the person and have them decline it.
This saves a lot of receptionist time during calls.