If you look at the Mobile offers at the moment... you have:
You Choose offered by Vodafone
Flexi Mytime/Anytime offered by Telecom
Both with minimum terms. One can assume that both are intended in locking a customer in for when number portability comes into affect. With things like local loop unbundling, number portability, and naked DSL (which may take some time before it is offered)... It wouldn't really surprise me if they* tried to do the same thing with broadband, calling promotions, and landlines.
* By the word they, I mean internet providers, toll providers, landline providers, mobile providers etc.
