I think Japan uses a CDMA network, but the UK uses GSM. So you need to know if you can put a GSM sim in a CDMA phone...

Call SoftBank and ask them about this and if they will unlock it. There's a process apple put in place for carriers to unlock iPhones so if you've paid off your contract with them they should do it without argument. You shouldn't need to jailbreak it. If the CDMA/GSM switch is not a problem you could then use any PAYG sim in the uk, ask for a micro sim or cut a normal down to size.

I wish people wouldn't respond to posts like this with "I think...". There is so much misinformation out there when it comes to subjects like these.

1. Au is the only major CDMA provider in Japan. Softbank and DoCoMo are GSM.
2. All iPhones since the 3GS (except for the Verizon iPhone 4 CDMA version) are universal and with few exceptions, and provided they are unlocked, will work almost anywhere.
3. Many carriers will unlock you iPhone once it's paid for. It's done through apple, and when you pay for the unlock, it will be unlocked the next time you plug it in to iTunes (I've personally done this in Canada with an iPhone 4 and then used the phone in Japan).
4. Softbank does NOT offer this service, even when your phone is paid for. Check here before you reply with a "well, they should.."
http://support.apple.com/kb/HT1937?view … cale=en_US
5. Jailbreaking can be done on most iPhones, as long as you haven't updated to iOS 5.1 yet.
6. Unlocking on your own requires jalibreaking. If you haven't updated to iOS 5.1 yet then you can jailbreak. BUT, if you've updated your phone in the last year or so, then your "baseband" software on the phone would have been upgraded and there is no software unlock that will work. I am 99% sure that your iPhone 4 cannot be unlocked.
7. There is one option left: the gevey sim. But it will also only work if you've not updated to iOS 5.1 yet. It also requires you to dial "112" -an emergency number- whenever you reboot your phone. Not cool.
http://www.iosnoops.com/2011/03/27/geve … -4-unlock/

The short answer is that no, it will not work in the UK. It is possible that someone will hack the phone one day to allow you to unlock it, but it's unlikely. The $75 alternative gevey sim method might work if you haven't updated your phone lately, but it's sketchy and will likely not work for long.

Take my advice and sell the phone in Japan before you move to the UK, and then buy a new one. You will be saving a lot of headache.

Yeah you can untethered jailbreak on iOS 5.1, and the latest gevey sim doesn't require you to call 112 (which actually isn't an emergency number in the UK, only in mainland Europe).

However, it's still definitely not worth the hassle - it's very hard to find a supplier of non-fake gevey sims, and the fake ones don't work; whereas it's very easy to sell your iPhone in Japan and buy a nearly new one from CEX when you get to the UK.

dtcamero wrote:

what about taking an unlocked american AT&T iphone to Japan...? SoftBank is the only iphone carrier over there right? so would they give me a sim card? Also would I be stuck with a 2-year plan or is there a month-to-month plan possible?

I think there might be prepaid SIMs, I can't recall with softbank. If there are, they don't include data plans. The only major problem you would have to worry about is dealing with making sure the network access information is set up properly. Carriers won't give you this information either even though its available on every freaking phone. Sometimes the phone can autodetect it though...

As to contract, I'm not sure. Canceling a 2 year plan is only like 8-9,000yen, last I recall + paying off whatever phone you got.

dtcamero wrote:

what about taking an unlocked american AT&T iphone to Japan...? SoftBank is the only iphone carrier over there right? so would they give me a sim card? Also would I be stuck with a 2-year plan or is there a month-to-month plan possible?

Au also carries the iPhone as of the end of 2011 with the release of the iPhone 4S. If you have an iPhone 4S you can look into seeing if it will work. Older iPhone 4 models are not "world phones" and will not work.
You can rent a sim card but it is VERY VERY expensive.

dtcamero wrote:

what about taking an unlocked american AT&T iphone to Japan...? SoftBank is the only iphone carrier over there right? so would they give me a sim card? Also would I be stuck with a 2-year plan or is there a month-to-month plan possible?

I stand corrected on gevey sim.

As for jail breaking iOS 5.1, I don't think there is a jailbreak released yet:
http://jailbreakhow.net/5.1-untethered- … -progress/

One other thing about this whole mess, if you ever sell your iphone in the UK, the buyer will inevitably update it using iTunes, brick it and complain to you and ebay. it's just not worth the hassle.

vix86 wrote:

dtcamero wrote:

what about taking an unlocked american AT&T iphone to Japan...? SoftBank is the only iphone carrier over there right? so would they give me a sim card? Also would I be stuck with a 2-year plan or is there a month-to-month plan possible?

I think there might be prepaid SIMs, I can't recall with softbank. If there are, they don't include data plans. The only major problem you would have to worry about is dealing with making sure the network access information is set up properly. Carriers won't give you this information either even though its available on every freaking phone. Sometimes the phone can autodetect it though...

As to contract, I'm not sure. Canceling a 2 year plan is only like 8-9,000yen, last I recall + paying off whatever phone you got.

I've used a Canadian factory unlocked iPhone with a pay-as-you-go sim card from SoftBank. It's a massive pain in the ass, requires jail breaking to get MMS working, is quite difficult to setup (because the prepaid sim card is not meant for iPhone and doesn't give the iPhone settings automatically for MMS, etc). It is impossible to use data in this way. And note that MMS is essential in Japan because SMS do not always work between carriers.

johnwalkr wrote:

kitakitsune wrote:

dtcamero wrote:

what about taking an unlocked american AT&T iphone to Japan...? SoftBank is the only iphone carrier over there right? so would they give me a sim card? Also would I be stuck with a 2-year plan or is there a month-to-month plan possible?

Softbank wouldn't even sell me a sim card for a Japanese iphone so I doubt it.

Correct. Softbank will not sell you a sim card for you iPhone, nor will they let you have a data plan for a phone that they did not provide.

Be careful here. it's technically possible to bring you unlocked phone over, and buy a cheap smartphone from SoftBank in order to obtain the data plan and a sim card. It's technically possible to use this sim card in your phone. But the contract states that this voids the data plan, and when they notice that the IMEI number of you phone doesn't match the one you bought from them, they can back charge you a per kilobyte cost per data that is very, very high. So don't do this.

Ya this is what i was thinking of doing, but was also really concerned about... I'm going to be there for 3 months, so I think I'll just go with AT&T's int'l data plans. an extra $99/mo gets you 275mb, which I'll need because gps alone is 30mb/hour...
Last year it was $200/mo for 200mb... before I knew I went over I had used 300mb and everything over the limit is standard rate $5/mb... so I came home to a $700 bill (talked them down to the plan's $200.)
Going over the limit is the scary thing, that $5/mb rate, and thankfully AT&T has now instituted another higher data plan, $200 for 800mb... which I can use as a safety net of sorts if I go over. And they're very flexible about letting you retroactively pick the appropriate plan based on how much data you actually used.
Ya I know it's rediculous, costs them little extra money to provide int'l service, and we're pretty much getting robbed... but at least we're getting robbed for a lot less than before.  Plus I know this will work and don't have to worry about the technical details.

dtcamero wrote:

*prices*

How much total a month, will all the extra stuff be to use your phone int'l? I'm ignoring how much you pay now cause I figure you'll want to use your phone when you get home ya?