Today's (apparently worldwide) problems with the Skype system meant that I couldn't use it for my conference calls, and I usually do. What do you do when that happens? Well, one thing I do is to always have active subscriptions to alternative VOIP services, so that if one isn't working, I can switch to another.
For one of my telecons today, I used Gizmo. That worked well. My only niggle with Gizmo is that, with the Linux version, it won't die when you try to close it, you have to kill the process. Otherwise, it was fine.
For a later telecon, I used JAJAH. The cool thing about JAJAH is that it phones you, you don't talk into a computer headset, just into the nearest landline or mobile phone. It's very useful if you are going to be near a landline where you can receive calls but can't make outgoing calls (especially long distance calls). JAJAH calls you first, then sets up a VOIP connection to the phone on the other end. On a 90 minute call today, it was perfect, you couldn't tell it was a VOIP call rather than a traditional long-distance call (UK to USA).
Skype is good most of the time, but it's definitely necessarily to have your alternatives planned out ahead of time.