Are you sure incoming calls in NZ are free? What I read says that the caller pays a high per-minute charge compared to a local call, definitely not free. This sounds like the common system of caller pays for airtime, vs. the North American system of cell phone owner pays for airtime.

Again, the problem is markets. The cell phone owner comparison shops for providers and negotiates rates. The caller does not, she only gets to decide whether to call or not. Any time the person negotiating the rate is not the person paying the rate you get a flawed market.

(Which is also the case in most countries where the carriers subsidize the cell phones, so the phones get features carriers like, and not so much the features that users like.)