How not to build your own Hosted PABX
Too many times it has been posted or brought up in conversations and forums all over the Internet, like this one
...install an image (sic, like elastix or trixbox) on a VPS (Virtual Private Server)
It is a clever solution. It will probably work more than 95% of the time. You will have to know what you are doing, and you will have to pay monthly VPS hosting rates. Quality of Service (QoS) will likely not been set up for voice traffic (update:May 2009), so the audio quality is likely to be affected for a word or two in every conversation. Not a big issue. In emergency situations, VoIP networks of this nature would be deemed a health hazard. There is a reason land lines have fixed addresses attached to them, and offer a triple-zero (000) emergency service.
What a hosted PBX service is
A hosted PBX system delivers PBX functionality as a service, available over the Public Service Telephone Network (PSTN) and/or the internet. Hosted PBXs are typically provided by the telephone company, using equipment located in the premises of the telephone company's exchange. This means the customer organization doesn't need to buy or install PBX equipment (generally the service is provided by a lease agreement) and the telephone company can (in some configurations) use the same switching equipment to service multiple PBX hosting accounts.
Instead of buying PBX equipment, users contract for PBX services from a hosted PBX service provider, a particular type of application service provider (ASP). The first hosted PBX service was very feature-rich compared to most premise-based systems of the time. In fact, some PBX functions, such as follow-me calling, appeared in a hosted service before they became available in hardware PBX equipment. Since that introduction, updates and new offerings from several companies have moved feature sets in both directions. Today, it is possible to get hosted PBX service that includes far more features than were available from the first systems of this class, or to contract with companies that provide less functionality for more simple needs.
In addition to the features available from premises-based PBX systems, hosted-PBX:
* Allows a single number to be presented for the entire company, despite its being geographically distributed. A company could even choose to have no premises, with workers connected from home using their domestic telephones but receiving the same features as any PBX user.
* Allows multimodal access, where employees access the network via a variety of telecommunications systems, including POTS, ISDN, cellular phones, and VOIP. This allows one extension to ring in multiple locations (either concurrently or sequentially).
* Supports integration with custom toll plans (that allow intra company calls, even from private premises, to be dialed at a cheaper rate) and integrated billing and accounting (where calls made on a private line but on the company's behalf are billed centrally to the company).
* Eliminates the need for companies to manage or pay for on-site hardware maintenance.