It does not seem that Econet Wireless New Zealand is positioning itself as Ewnz, though the abbreviation is used in news etc for them.
It seems like they don't even have a website for NZ and operate from central econetwireless.com
If they'd decide to promote themselves as ewnz, then still the potential of the domain would be limited as you'd be needing them as much as they'd need you. I.e., the only end user, probably. Hence the value could be $50 and could be $10000. Good luck.