Hosted PBX is the idea that your service providers hosts your phone system for you. Then over an IP unification you are adjoining to that service provider. You don’t hit to control anything. you only block ini your IP phone.
Who is old with this concept?
I am familiar with the concept of hosted PBX.
Here are a couple VoIP services that provide hosted PBX:
Packet8
RingCentral
Also, InPhonex provides Unlimited USA/Canada Business VoIP service and will sell you the Linksys SPA-9000 IP-PBX adapter and IP-Phones for creating your own in-house small business IP-PBX system.