Multi-office practices, or even a single office, can reduce workload for administrative staff by using a call center. It's vital, though, to have a single appointment database with shared access via the Web. That way, everyone who views the schedule is looking at the same thing. And the moment an appointment is made, it's no longer visible to anyone else.
Some appointment systems require installing software on your network. Others, such as TimeTrade, require no installation - they're Web self-service, so you just log in to use it from wherever you are.