Talk about future-proofing! The designs that Mr. Bell produced in 1876 survived for close to 140 years with hardly any changes. There were adaptations and refinements aplenty by legions of engineers and companies around the globe but those were so minor in the schemes of things that they hardly matter. The switches were reduced in size and changed from mechanisms driven by electro-magnets to capacitors and then to integrated chips. The inter-exchange connections changed from copper to fibre and world-circling satellites. Minor changes these, of hardly any consequence. The handset retained its shape and functionality, although the rotary dial did manage to get replaced by buttons.
The revolution came with mobile phones using time division multiplexing for managing cellular bandwidth and lots of other technical jargon that I don't think copy/pasting from various web pages would add much value to the gist of this post.
Cellular phones have - as yet - not changed the legacy systems; those that are called fixed or land-line phones. These shall remain pretty much unchanged in the near future or at least till everyone replaces them with Star Trek style communicators.
I don't have to be particularly old to remember the days when offices did not have extensions but each set was connected to its own unique line stretching all the way to the phone company.
The engineering refinements boon was allowing a complete exchange to fit within a single shelf and the Private Branch Exchange (yes, that's what the abbreviation stands for) was born. Suddenly, everyone wanted one so went out and bought one. No business, hotel or school could operate without one. The advantages of a local exchange for a location, or even spread out geographically, can not be argued against.
The revolutions to the PBX design came with the invention of the PC-based exchange and later with IP telephony. These offered unparalleled ease of use and the ability to quickly implement changes.
The differences to analogue and details of operation of Voice over IP are many. But, when all is said and done, you still pick up the familiar handset and press the same buttons to dial. (When no one is around, I try speaking to my phone to dial various numbers but it always replies that it doesn't know the current time on Mars.)
VoIP PBXes have two key features: First, they convert sounds to and from data packets, and secondly, can connect to other similar exchanges not via the lines coming from the phone company, but over the Internet (or leased line).
They save on call charges and phone wiring, as well as being scalable and easy to manage. The perfect fit for businesses.
Being quite enamoured with VoIP (read: geek), I once connected my mobile phone to a software-based PBX so any number dialled from the phone would place a call by switching it to a second software PBX, then to a VoIP provided by my phone company, then to PSTN lines to finally land at my other land-line phone. (Say what you will, I still think that was pretty cool.)
When the time came for me to evaluate and obtain a PBX for the company that I worked for, I truly was leaning heavily towards a VoIP solution and tried every excuse to justify it to myself. In the end, I decided against it and went with a non-VoIP digital PBX.
The reasons for not selecting a VoIP solution were based on the traditional reasons quoted in favour of doing so. Let's go over them one by one.
Ease of Installation
This includes installation not just of the PBX itself, but the wiring and the sets. For both types, pretty much the same types of screws are used to nail it to any handy surface, the same ducts are used to pull the cables and the same snickity sound when you plug the handset into the wall. I can't say about the PBX in your office that perhaps fell off a truck and needed a doctorate in engineering to configure, but mine came with a nifty program for Windows that allowed me to make it do everything but the dishes.
Free calls to branch offices
Yes, I'll give you that. On the other hand, I didn't have a branch office. And if I did, I could have installed an IP trunk card in it to achieve the same.
Cost saving over VoIP providers
This changes from provider to provider in each country. I only know the rates of my VoIP and PSTN providers; the rates are identical when calling other land-line or cellular phones.
Eliminate phone wiring
I have never been able to quite understand why this is quoted as an advantage. Firstly, the sets don't connect over WiFi (well, some do), but anyway, secondly, Ethernet cabling is triple the cost of traditional phone cables even without adding the cost of routers and switches.
Eliminate vendor lock in
Non-VoIP PBXes use an extra pair of wires to provide features to handsets such as smart-button programming. The PBX recommends which handsets are compatible. Sets from other vendors would probably not be. However, this was the key reason for not choosing a VoIP PBX; the handsets with displays and extra buttons are expensive - although the VoIP versions were even more so. On the other hand, within the office were a large number of positions where feature sets were not to be installed. Simple handsets - such as the ones in homes - sell for $25 dollars while the propriety sets start from $100. As mentioned, the VoIP versions are slightly more expensive starting from about $120.
A simple observation on how people use their office phones shows that 99% don't know - and refuse to learn - how to program the quick dial buttons while the other 1% forget the latest programming that they did and so everyone keeps a printed list of extension numbers posted on their desks and dial number manually.
In any case, just multiply the $75 difference in the handset cost by the number of users in your company to see the effect of this 'cost saving'.
Scalability
The non-VoIP PBXes go up to a few hundred external and internal connections. A better question is: How many external and internal connections are your requirement?
Better customer service
Can you really increase productivity and service to your customer if you can integrate your PBX to your computer? From experience of call centres, my answer is an absolute yes. On the other hand, if your company doesn't have a call centre then this becomes a moot point.
Add features
The feature list normally quoted is the same as that which I was getting with a non-VoIP PBX. Look closely in your PBX's manual, you probably have it too.
SIP phones are easier to use
Again, a definite yes. User do not need to learn key combinations as they get a GUI on their PC for setting up conference calls, etc. Do note that this means using your PC as a device and a headset. My users (other than the call centre ones) wanted a phone set on the table. Perhaps all of your users are more comfortable with headsets, I can't say.
Conclusion
Don't get me wrong; I love to be on the bleeding edge of technology, but when that means using corporate funds to scratch that itch without my users getting any benefit, that is what I do not agree with.
When looking at call costs all the other features could be easily discounted with in the argument for and against VoIP PBXes until the recent past when most countries did away with inter-city call costs and brought them down to the same as the cost of a local call. International call costs are still high (except for among some countries) but that still doesn't make a case for a VoIP PBX as the same can be achieved by adding a SIP trunk card to your PBX.
