I've been trying out Skype, the internet-based phone system I commented on last week (read post).
It is very good! The best thing is that if you call another Skype user, that call is 100% free, wherever in the world the other party is located. If you call someone on a normal landline or mobile phone, you have to pay (you buy credit from Skype) but the rates are very low compared with what you'd expect to pay using a normal phone. For instance, a call to the UK or the US costs €0.02 (that's two Eurocents) a minute; a call to a country like Costa Rica is just under €0.06 a minute. These are the rates wherever you are.
Sound quality on calls is excellent, especially if you use a digital microphone/headset combo.
I recommend everyone to go to Skype, download the software right now and set up an account. You'll notice an immediate positive result in your phone bills!