Updated: 10/09/2009: At the moment an official one doesn’t exist because Telecom aren’t an official supplier.
The Carrier Bundles contain a number of different things including voicemail number, carrier logos, apns etc etc. Using *5005*86*voicemailnumber# doesn’t update the voicemail button so a Carrier Bundle is required.
With XT Logo
Here is the Carrier Bundle – Telecom_nz.ipcc – updated 10/07/09
See Install Instructions @ http://www.unlockit.co.nz/forum/index.php/topic,4.0.html