For someone to call you from a landline you need to get a Skype number. You can get it monthly or pay by the year. Only problem is that they offer them for a limited number of countries and New Zealand might not be one of them. You should check out the Skype site, they offer a lot of new "options" nowadays but not every one is for all countries.
For SMS, you send them from the app, there's a small charge per SMS and the person you sent it to can reply to your messages without dialing a number. They can't initiate the SMS from a phone to Skype.
I'm really not sure if all of this would be "cheaper" than a phone plan within your home country, I use it for contacting family that are over on your side of the Pacific. For that, it's much cheaper than a phone plan here seeing as it's occasional. Like I said above, you should check out their site...