On my old Motorola Q9C there was a feature that adjusted the ringer profile according to my Outlook calendar. When set to Automatic the ringers and alerts would silence during any time shown as "Busy" in Outlook.

For the Pre, the personality would only change if the ringer switch was on meaning that it would not override the phone if it was in the vibrate position.

Options would be as simple as:

Disabled or Enabled

If enabled then:

Vibrate - calendar shows busy phone will silence and vibrate in accordance with seleted alert/notifications (if sms, email, phone produces audio normally then the phone will vibrate).

or

Silence - no alerts or notifications effect the phone

or

Visual - screen illuminates and shows SMS, email, calls, etc.

Then when calendar shows "available" the default system will be in effect.