I think I've posted something of a similar nature here, a few months ago.
Im living in japan and bought an iphone4 from softbank. its awesome, as most of you reading this will know. Im assuming i'll be able to use my phone in NZ when i come home in august. Some say the softbank phones are software locked to softbank, but mines been jailbroken since just after I got it, and hopefully this wont be an issue. the phone runs on an edge network here i believe.
I have an unlimited data plan here with softbank, and i pay the equivalent of about 70 bucks a month for unlimited data and a normal calling plan. Im probably being hopeful but is there anything around back home that has unlimited data? or am I dreaming. If not, that really sux.
also i have a usb 3g modem i bought from softbank, it runs on a sim card too.. i wonder if i can use it with a provider back home.. this question may be a lot more difficult to answer however.
gonna be gutted if its going to cost me a fortune to run my iphone at home.. or if i cant use it. surely I can use it.
Anyway thanks for your time team.