Can Hosted PBX VOIP telecom systems actually cut down on my business telephony expenses?

Your experience is likely to be determined by the connection to the hosting site.

Reliability, latency, and quality of service (queuing strategy) are major factors in how well the service is implemented.

My point being: don't skimp on the data connection. I've seen lots of people try to run VoIP over a VPN and just crash and burn.