You will want to be sure that your network is healthy. Your cable plant is a big area to check as well as your active electronics on the infrastructure. They should be running healthy and error free. Many of the VoIP manufacturers will audit the active electronics, but you also want to check your cabling to be sure that it tests to category 5e specification. If it is faulty you will have a slew of problems.
You will also want to run your own cost models to determine what type of phone to use (the more expensive one without a switch and the less expensive one with a switch). Depending on what type of electronics you have, it may be much less expensive to keep the switch in the closet. Make sure it has sufficient power backup or your phones won't work in a power failure. You can use Power over Ethernet (PoE) to accomplish powering the phones over the data cable.
Finally be very careful to check to be sure it will really provide a savings. In some countries the increased data circuit size is cost prohibitive. I was in one country not too long ago and a fractional T-1 line was $6,000 per month. Weigh all the costs! You may want to check out this article .
This was first published in March 2006