5. I've heard that I'll have to forklift all of my network equipment in order to use VoIP in my organization. Even if I can save on telecom expenses by switching, is it really worth it to lay out a bunch of cash for new switches and routers?
The answer to this question depends on how much VoIP you plan to implement. You can save money by switching your phone service to VoIP, while keeping your in-house PBX in the legacy realm for a few more years. You may also save money and gain features by migrating your in-house digital phones over to an all-IP Ethernet network. Sometimes, you'll save money with one approach, but not with the other. One under-hyped aspect of IP telephony is that you can migrate "a little at a time."
If you plan to go "all the way" (that is, IP phones on your LANs replacing all your organization's legacy phones), your networking equipment will need to be up to snuff. Switches and routers need to support quality of service (QoS) measures--special protocols whose goal is to ensure that the quality of VoIP phone calls never suffers because of a computer virus or spam swamping your network's capacity. The first step to figuring out how much new networking equipment you need, if any, is to audit the capabilities of your network's routers and switches. Such an audit will reveal the cost of converging your network and allow you to better justify (or rule out) a switch to VoIP.
6. Some people have told me I can save my company money by implementing an open source phone system like Asterisk or SipX, but I'm concerned about the security and stability of open source software. Are open source phone systems really comparable to the big commercial ones?
Many enterprise telecom admins don't even realize that a plethora of highly stable, open source telephony software exists. Ask a typical IT manager what he thinks of when you say "free VoIP software," and he'll probably tell you, "Skype," which is neither open source nor (completely) free. In response, I'll suggest a turnkey solution based on Asterisk, say. But since open source solutions have been stigmatized as insecure, unstable, and unsupported, the reflex reaction of my clients is, "Whoa, don't try to put that on my network."
Caution is helpful, but paranoia is unwarranted. If you have a qualified consultant or hands-on engineer build and maintain your PBX on a well-hardened Linux or BSD server, your phone system's central nervous system can be at least as stable as an old-school PBX chassis, and perhaps more so. With a reasonable amount of failover provisioning--i.e., hot-swappable hard disks (or a diskless, flash-based server) and redundant power supplies--a soft-based PBX can yield even higher hardware availability than a traditional commercial PBX system.
But all of this is academic, though. In order for an open source PBX solution to be stable, robust, and reliable, it needs to be built and maintained by a qualified support staff. That's a truth that applies to all phone systems, old and new, open source or commercial. Whether or that staff is in-house depends on how you do business, which leads me to question #7.