Will you need to support remote users that are working outside your headquarters office?

One of the big advantages of VOIP is being able to take a phone and connect it anywhere on the Internet and have it work as if it is sitting in your office. But to get to this point, you need a VOIP PBX that can support remote users. In some cases, you will need a phone that has a built-in VPN client (Snom.com sells such IP phones, for example) to connect to your corporate network, just like a remote PC user. Some of the lower-grade VOIP PBXs, such as the Linksys SPA9000, can't currently support this configuration; all the phones connected to it must be on the local network.

What will you do with your existing analog phones?

If you have inbound fax lines and analog answering machines that you can't or won't get rid of, you need to figure out a plan for either keeping these lines or substituting work-arounds to continue using these phones. The VOIP PBXs also vary in their support for inbound analog lines, something that is also worth investigating. Speaking of phones, prices on digital phones continue to drop and Polycom Inc. has IP phones that cost less than $US150. "This makes it easier for our clients to capture the total cost of VOIP ownership and savings from month one," says Agate.

Can you keep your existing inbound phone numbers?

Some VOIP providers can transfer some of the phone numbers to the new digital lines, some can't. It's worth checking. There are many reasons why they can't be transferred -- some political, some technical -- but if you need to keep your existing numbers you may have to continue to pay your local phone company for minimal service for these lines.

Do you need to upgrade your network switches and routers?

One of the biggest issues with VOIP is in understanding how quality of service (QoS) is specified and delivered across your network infrastructure. Voice quality is directly related to network latency and packet delays that can cause drop-outs and degrade overall audio. "We have heard horror stories about other VARs that were really good data guys, but they didn't understand latency issues and other things that affect voice quality," says Agate.

If you haven't paid much attention to QoS before, you will need to spend some time understanding the issues. Several of the better VOIP consultants should be able to help you with this. If your switches are aging, it might be a good time to replace them as part of the VOIP project anyway.

A second issue is whether you want to deploy Power over Ethernet to power your new digital phones. Sure, you can plug them into a wall socket, but that might not be convenient or as reliable as having them get their power from a central wiring closet that has battery backup in case of power failures. Here again, you may be looking at buying new switches to handle this.

Do you really need to own your own IP PBX?

You might be able to get away with a lower-cost hosting solution, whereby a VOIP provider rents you space on its own PBX and all you need is an Internet connection and phones. As your needs grow, you can migrate to owning your own PBX later on. VirtualPBX.com, M5Net.com, Bandwidth.com and several others offer hosting solutions.

Don't do everything at once

One final bit of advice is that it might help to get your feet wet with VOIP and to tackle the project in several stages. Agate suggests that IT managers start off small by deploying VOIP on the local network first, then incorporating a hybrid of digital and analog terminations. "Then move slowly, using VOIP just for outbound traffic next." One alternative is to make use of Skype Ltd. for business and use PCs with its software to make outbound calls. Alternatively, you can make use of one of the many services such as TalkPlus.com, Rebtel.com or Jajah.com that will assign an international number to your existing phone. These methods are especially attractive if you presently spend a lot of money on international long distance.

As you can see, there are lots of things that revolve around a VOIP deployment. But if you think of this as any other major infrastructure rollout, it should go a lot smoother.

David Strom is a writer, editor, public speaker, blogging coach and consultant. He is a former editor in chief of Network Computing and Tom's Hardware and has his own blog at strominator.com. He can be reached at david@strom.com.