Because the mobile networks are different. You will have to use a local (NZ) mobile network if you want to use the phone in NZ.
the iphone the iphone
No, T-mobile does not have the iPhone. AT&T has it though.
There will not be an iPhone 4S for T-Mobile but you can get any iphone unlocked at unlockatt.com
Dial the NZ mobile number exactly the same way you do when it is in NZ.
T-Mobile does not have the Iphone only At&t does
call his/her mobile(iphone) or sms
You can use a iphone for boost mobile just jailbreak it and downlaod ultrasn0w
iPhone 4 can
For iPhone, it was iStone. I have it on my iphone 5 and had it on my ORIGINAL iPhone
he used iphone.....