New office, New Phone system, Newbie Help!

[Preqin]

Right, as you may have read in my welcome post, I am a sys admin for a firm of around 40 people, with an office move on the cards in around a couple of months.

This new office is not serviced, i.e. we are on our own, which gives us a chance to set up our own phone system.

At present we have 'standard' land lines provided by our serviced office and we are using a nasty combination of VOIP Cheap and Skype. The cost savings initially were a huge benefit, but to be honest its now more trouble than its worth - topping up is causing major issues, people seem to have stigma attached to it because they are using 'toy' phones as some seem to think etc.

I understand from the home page that we would fall in to the "Centrex" bracket - how exactly does this work?

The initial plan was we would get a server or something that basically chose voip or pbx depending on cost and what ever was available, I'm not sure if that's "Centrex" or not.

My main worry is the drain on the internet bandwidth, and what happens when the internet is down?

If someone could point me in the direction of some detailed literature in this vein it would be appreciated!

As a very ruff guide, what sort of options and costings (instalation) would we be looking at for a 40 employee firm where everyone needed a phone?