Here's the trick behind the closure of Telecom's TDMA/AMPS network on 31 March 2007 (17:00 local time) and the introduction of Number Portability in New Zealand on 1 April 2007:
Everybody will be able to change their service between Vodafone NZ and Telecom NZ and keep their existing number (including the prefix 021 or 027) after April 1st 2007. The trick behind Telecom shutting down their TDMA system a few hours before MNP becomes their legal obligation is that 025 numbers (TDMA/AMPS numbers) won't fall into their MNP obligation.
What they offer now is that Telecom TDMA/AMPS users (025 users) can upgrade to CDMA (with a free Nokia 211
and, if available, they can keep their number and just change to the 027 (CDMA) prefix. But this is not enough, as one can say that a former TDMA/AMPS customer can move as easily to Vodafone and ask them for the same number with Vodafone's prefix (021), but here's Telecom's trick to keep TDMA/AMPS customers with them, first they close the network one day before MNP so they are not obliged to offer portability on 025 numbers and second they offer a free call diversion to the new 027 number, ONLY to customers who choose to stay with Telecom and not move to Vodafone!
This means that on the one hand the 025 numbers are legally considered obsolete after March 31 and so they can't be ported to Vodafone, but if the TDMA/AMPS customer chooses to opt for Telecom's upgrade-to-CDMA offer they get all their calls diverted for free to their new 027 number, i.e. the 025 numbers will still appear to be working for them, although legally it will be a "diversion" to the new number!
In my opinion this is very nasty on Telecom's behalf as it blackmails users of the old 025 network to stay with Telecom and cancels their legal right to MNP after April 1st 2007....