The reason is, dialing "0" tells the telephone-computer "I want to go to the national level and make a selection from available area codes" while dialing "011" (in your case; in NZ we dial "00") means "I want to go to the international level, make a selection from available country codes, and then make a selection from available area codes".

I can provide Skype tutorials and/or propaganda as necessary, just say the word. <snips evangelism> But yay for phone calls! Whenever I was overseas it always meant a huge amount to hear a voice from home.