There's way more to it. For 50 users, it's probably not a cost effective solution to set up from scratch.
First: Look at the equipment you already have: Unless it's fairly new, and running fairly recent code, chances are you'll need to replace some of it. Proper network qualification is CRITICAL to a successful implementation> you need to do end-to-end evaluation of bandwidth and latencies both total latency and latency variation - jitter-.
Next: Look at the skill set of the people charged with setting up and maintaining the system. There is a huge learning curve for "phone people" to pick up data networking practical concepts: the curve is at least as steep going the other way - data people (generally) have no idea what goes on behind the telephone. Dial plans are critical, E911 planning is critical, backup POTS/ISDN planning is necessary, QOS is vital to proper operation.
Commercial IP telephony doesn't work through the Internet - to many possible/probable variables.
There are some local telcos that are offering IP Centrex, that might be a good way to go for you: basically all the magic parts of the IP Telephony stuff is in the Telco, you get IP Phones, they get the headaches.
Commercial IP Telephony is a long way from "Plug & Play:" Any money you are going to save is nothing compared to the consultant's fees, software, and hardware upgrades (and the circuit upgrades, and and and ....)
You could get started with VOIP using your existing analog phones, and PBX.
YOu would choose a gateway that could handle the load to your PBX, say 1 or 2 T-1's . A 3600, 5350, 3700, 4224 could get you started. All you need then is a couple routers for gateways, some T-1 modules, a bunch of analog modules. You could use ITS( IOS telphony service) on a router to service a few IP phones and still connect to your PBX and the PSTN thru a T-1.
Now if you had a IP link to remote offices, you could send VOIP calls over your existing IP links and save on toll calls interoffice.
This would save $$$ every month since you pay a flat rate for your IP links already, and you could just bump it up a little and put some VOIP traffic on there.
You could then take step 2 and get the call manager MCS, and a bunch of IP phones, and some analog gateways like ATA to connect fax machines to the network. Step 3 you would eliminate all PBX, and all analog phones, and use IP messaging along with your IP telephony with the Unity box.
IP telephony will always save you $$$ in the long run. Make sure you purchase a service contract so that you get the wrold class TAC support team!
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...