A huge advantage was bypassing the ridiculously high tolls charged by the providers of our day to day telephonic communications services such as Telstra/Telcom/Bell et al. It is super cheap .. most western countries can be called for about .17 Euro cents /minute or about 4 cents NZ/min. Pretty cheap huh?
So what's the catch? None really, you download the program (Skype), install it, go online and deposit funds to your Skype Account and dial away. It really is just like using a telephone.
You pay for calls to phones from your computer but calls to other Skype users (on their computer) are completely free. You can have conference calls, send files, text messages etc. This is just like Teamspeak but has the added option of calling a normal telephone/mobile anywhere in the world.
I recommend using a headset plugged into your computer so that the microphone moves with you and stays in front of your mouth just like a normal telephone handset would. Get it at Skype
If you'd like to have a chat on Skype my user name is bradleymarsh. TTYS :D