how to change carrier?

[dbmnk]

I have brought my iPhone 3 back from Japan and want to use it with a homeland carrier. It is presently locked to the Softbank carrier SIM card, I believe.
What do I have to do in order to change the SIM card to another and be able to use the phone?

 

[Zermelo]

I have brought my iPhone 3 back from Japan and want to use it with a homeland carrier. It is presently locked to the Softbank carrier SIM card, I believe.
What do I have to do in order to change the SIM card to another and be able to use the phone?

You obviously have to unlock it. First check what FW you have. If it's 4.1 or less then you can jailbreak it without problems. After that you have to unlock it. Go to Settings -> General -> About -> and look at your modem firmware. If it's 05.13.04 or less, you can currently unlock it with ultrasn0w from cydia which will appear on your screen after you jailbreak it.

 

[andy9l]

I'm not sure if it's the same in Japan, but here in the UK you can contact your provider and have them unlock your phone officially (through Apple/iTunes). You will have to continue paying the remainder of your contract.

 

[dbmnk]

So you're are saying I will have to jailbreak it, and then be lucky with the modem firmware?

The iOS is version 4.2.1. Is it at present possible to jailbreak it and do what I want, or do I have to wait for something?

I read on Dev-Team Blog that it should be possible to jailbreak 4.2.1 at present, but maybe I am missing something (it's an iP3).

What is the difference on redsn0w and ultrasn0w?

Softbank doesn't do unlock - even though you've paid the phone in full - cheeky bstrds.