Over time, I realized that there are a few advantages to using Skype. First, it doesn't tend to record the same kind of line noise as you get on a standard phone. When working with old fashioned phone recordings, I almost always had to add a filter to eliminate sound that was over 3KHz or below 300KHz. Telephones don't actually transmit anything outside of those ranges, so anything else you pick up on a recording is noise. But I've noticed that applying that filter on Skype calls doesn't change much, which would indicate there's not much noise.
On the down side, Skype calls are digital calls sent over the internet. As such, if you have bandwidth problems or dropped packets, you can wind up with glitches that make the call sound like a bad cellphone call. But there are ways to minimize those problems. The Conversation Network's Doug Kaye and Paul Figgiani have put together an extensive video explaining how to configure Skype for the best possible results. And when I say extensive, I mean it. The video weighs in at 22 minutes, but it's well worth watching.
Some of the tips are no-brainers, like shut down other applications on your computer when making calls. But the advice on configuring your firewall is pretty useful.