Is voicemail good enough?
Voicemail works when your callers are patient and already customers. It fails hardest with first-time callers, who are the expensive ones to lose.
Do people still leave voicemails?
Existing customers often will. First-time callers frequently will not, because they have no relationship with you and another number is one tap away.
This is why voicemail feels adequate from inside the business. The messages you do get are from people who were always going to reach you.
What does voicemail cost you?
The enquiries that never became a message, which by definition you cannot count. The second cost is that voicemails arrive unsorted, so an urgent customer sits in the same queue as a sales call.
When is voicemail actually fine?
When your work is nearly all repeat and referral, when nothing is urgent, and when you return calls the same day. That describes a real category of business and those businesses should not be sold anything else.