Not sure how call park would solve anything for answering incoming calls. It sounds like they need an auto attendant. If they don't want voice mail, you could just not forward extensions to a mailbox. The only other option I can think of is to install an answering machine to one of the single line ports, but it will only take messages if the calls are unanswered. Sorry if this was no help.

"I thought I was wrong once, but I was mistaken"