Sorry about the delay in answering. If your Son has taken a laptop or will be going to cyber cafes to pick up E- mail ,he plugs phone in to a usb port and the connection happens by you and him using the internet at the same time - easy peasy. Lots of people do this, call friends and family back for very litle or no cost to especially the States. You could send a phone ahead to a pre arranged destination for him to collect if you choose tesco or probably betterfor him to pick up a skype phone there, no post or courier cost and less stressful( will it be there when he is?)
The campsites that we stayed on in NZ were really helpful with this kind of stuff . I also went on ask.co.uk
to find out how to get a cell phone connection in NZ, no joy with number protocol but loads of calling card offers that might be worth a trawl for you!