Have seen Skype mentioned here several times, starting a dedicated thread.

I just did a fairly quick (~10 minute) search online and was overwhelmed with information. What are the most important things to keep in mind? Some specific questions I have are:

Do you have to be close to a computer to make calls?

What is the sound quality and responsiveness like? I saw someone mention delayed transmissions, "like a satellite interview."

What is the real cost?

What kind of phones can you use? What phone features are most important?

Do you use a new phone number, an existing number, or your choice?

Is Skype a replacement for either a land line or cell phone, or a cheaper additional option?

Etc. etc. etc. All info appreciated.