Small Business On Premise PBX system

Is this a good Deal?Right now our phone bill is around $300 a month.  I just got off the phone with a salesman from Image-X, and he stated he can get me on VOIP system for $150 a month.  I told him I have seen other VOIP systems advertising for $40 dollars a month, and what would make me go with there system for $150 a month.  He stated not to believe everything you read, and advised me there was a catch to there system.  If it was Hosted VOIP system, more than likely it was $40 per phone, and if I had 10 people using a phone that would make it $400 a month.  Is this true? Then he stated if it is On Premise PBX system, it would be more reasonable, but the not to forget to include the cost of the PBX system, installation, configuration, and maintenance which could retail from $2000 to $20000.  That just sounds hard to believe, and not a very cost effective solution.Then like every salesman he went to explaining what his company offers.  He stated they would provide us with our own PBX system, along with phones, a voicemail server, and VPN router.  Setup, installation, configuration, and maintenance was all included with the $150 a month.  So then I asked him is there an additional per month cost to add a phone to the system.  He stated no, the only cost would be the purchase of a new phone and that we could have up to 20 people all on the phone at the same time as long as our bandwidth could handle.  He then stated after our contract is up, unlike most companies, you get to keep all the hardware.  Is this a good deal or is there some sort of catch?