How to subscribe to Message and VoiceMail events at account level?

There is no account level for SMS and Voicemail message notifications (even with reading). However, as a super admin role, you can subscribe for SMS and Voicemail event notification for other user extensions. You will need to read extensions to get the extension id of all or particular extensions you want to get notifications, then subscribe for the subscription with an array of event filters for the user extensions as shown in the example below.

var eventFilter = [
    /restapi/v1.0/account/~/extension/{extId-1}/voicemail,
    /restapi/v1.0/account/~/extension/{extId-2}/voicemail,
    /restapi/v1.0/account/~/extension/{extId-n}/voicemail,
    ...
    /restapi/v1.0/account/~/extension/{extId-1}/message-store/instant?type=SMS,
    /restapi/v1.0/account/~/extension/{extId-2}/message-store/instant?type=SMS,
    /restapi/v1.0/account/~/extension/{extId-n}/message-store/instant?type=SMS
]