One calendar for all users – exchange

I am looking for a way to associate one calendar with everyone in my department’s exchange account. It needs to be the default calendar for everyone because we rarely use our computer to see our appointments. We all use windows mobile on our phones, or web access, and can’t open shared calendars. If we could have our phones sync with two exchange accounts, that would work too. One syncs our personal email, the other would only sync calendar and tasks. Any ideas would be nice.