But there are some potential downsides. Since Skype shares some of its customers' network resources, some ISPs prohibit its use (some ISPs might block VoIP altogether, actually). For example, Skype could designate your business's PC as a supernode--a sort of peer-to-peer server for Skype traffic. I have read reports of some users whose networks were overwhelmed by sharing requests from the Skype network until they adjusted their connection, putting it behind a firewall.
How does the audio quality compare to that of a conventional landline? That depends on your Internet connection and audio device. I've gotten the best sound quality from a USB headset, because its digital connection is superior to the analog technology of older headsets. You can also plug in an analog headset to your PC's sound card or purchase a USB interface box to plug in your existing telephone.
At first, I noticed a bit of digital stutter on the calls, but I was able to eliminate this problem by installing an expansion card with a better USB controller. On some SkypeOut calls, people at the other end told me my voice sounded faint. The sound quality when using Skype to call another Skype user was usually excellent--better, in fact, than usual telephone service. A bonus: Skype-to-Skype calls are always free.
In general, business users will likely want better services than those Skype currently offers--for example, consolidated reporting of calls within the group. However, Skype can save you money if you're willing to put up with the odd glitch and a lack of business-level call reporting.