I need a LAN messenger

[ictponder]

Hoping someone here might be able to help. Yes, I've googled it...a lot!

Small business with 13 or so computers and I want to have an always on, public messenger that does not require a personal login. If someone calls and needs to speak with someone who is busy, whoever is fielding the call can simply post a message and it will propagate to all other workstations and anyone can check messages, read and clear them.

We currently have local voicemail and all employees have a google voice account attached to local vm extensions so a vm can be sent directly to their cell but this isn't always the fastest way to send a message. Email is currently our best option but it requires a login and sometimes a logout first as all the workstations as shared.