***We have now added these fixes to Installer!! It is now easier than ever to apply these fixes to your iPhone. See this post.***
(See www.kiwi-ise.co.nz for details).
1) Fixed CallerID: Incoming calls and text messages will now be recognised if the number is in your contacts.
2) Fixed iPhones phone number formatting (Contact's phone numbers, unrecognised numbers, dialing out): To go along with the CallerID fix I also edited the nz section in my UIPhoneFormats.plist so that numbers in your contacts, unrecognised numbers received, dialed numbers are all formatted correctly.
3) Added Carrier bundle for Vodafone NZ:
I have just finished putting together a proper Carrier bundle for Vodafone NZ. What this means is that you get a Vodafone Logo (I have created 2 versions "Full" & "Mini" and retained the original text-only version - you can create your own logos to use):

... and also, this bundle adds a new Services menu for Vodafone NZ under Settings->Phone ... it's not much but it just means it that Vodafone NZ is now set up as a proper carrier in the iPhone. I won't insert an image of the menu here but you can view it here.
I should add: THIS IS ~NOT~ AN OFFICIAL VODAFONE NZ BUNDLE! - I have created this myself based on the existing bundles.
I have updated the zip file with the new Carrier bundle and added some instructions on how to upload and configure it. BEWARE: You need to know how to SSH in to your phone and run commands via the command line.
4) Removed Annoying "Call Forwarding Active" Message: Edited carrier.plist file to get rid of the annoying "Call Forwarding Active" message that pops up when making or receiving a call - found in /System/Library/Carrier Bundles/Unknown.bundle/ (just change ShowCallForwarded and ShowCallForwarding values to false)
*** nzbullet has very kindly supplied some more great hacks (love the NZ Maps icon one!): ***
5) Set "Voicemail" Button to Call Vodafone Voicemail: As Vodafone doesn't have Visual Voicemail like AT&T, we can make use of that otherwise redundant button by making it call 707 when pushed!
6) ".co.nz" Keyboard: Replace .com on your keyboard with ".co.nz" or "com.au".
7) NZ Icon for "Maps.app": Change the maps icon to be more "nz friendly"

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8) Replace Blank "Edge" Status Icon: In NZ we get a blank blue box when connected to GPRS. Here's some alternative icons.
IMPORTANT: iBrickr/iFuntastic/iPhoneBrowser FIX:
If you plan on using either iBrickr, iFuntastic or iPhoneBrowser to upload these files to your phone then you will need to install the "Ziphone iBrickr Fix". This adds the AFC2 support which is lacking in the ziPhone jailbreak tool. If you are going to use an SFTP client then you don't need to do this - you would only need to install OpenSSH from Installer.
1) Go to installer and add this source: http//i.unlock.no
2) Click the "install" button in Installer and scroll to "Unlocking Tools" and download and install the "Ziphone iBrickr Fix"
3) Once complete, exit installer and reboot youriPhone.
When you plug your iPhone in you will now have file access through iBrickr/iFuntastic/iPhoneBrowser