Before you rush down the Skype route, have a look at
www.internetcalls.com (I've used this for almost 3 years now).
Less intrusive than Skype, FREE local calls to 30 countries approx INCLUDING USA, UK, Australia / NZ, China, most of Western Europe etc...
I like Skype too, but I like the FREE calls and cheap sms of internetcalls too... (and prefer it).