yes I was also thinking about hunt groups
I use one hunt group for immediate ringing on a bunch of phones that have no voice mail, and I FNA that hunt group to FNA after 4 rings to a second hunt group that appears on the rest of the staff's phones who have Voice mail. which creates a hunt group with delayed ringing on the admin staff phones.
When the manager starts to get too many calls ringing in his office to answer, he can encourage the floor staff to answer the phones sooner.
I have never had a complaint that calls are being dumped into the wrong mail box. but in this case I don't think they get the chance to ring forever either