Google's Nexus 5, at 39,800 Yen from the Google Play Store, is a steal. The phone will run the latest version of Android for the forseeable future (~next 2 years anyway), comes with Qualcomm's latest Snapdragon 800 quad-core processor, an improved camera over previous Nexus phones, and the deal-maker: LTE connectivity. The Nexus 5 (international version) supports LTE Bands 1/3/5/7/8/20. Band 1 will give you connectivity on both Docomo and Softbank; Band 3 will give you connectivity on Softbank, and in future on Docomo too. Japan Mobile Tech has some good info on how to use the Nexus 5 with a Docomo Xi LTE SIM, so I am going to provide some info on how to do the same with Softbank LTE.
The main problem with Softbank is they will NOT sell you a SIM-only contract that does LTE. You can get a SIM-only 3G contract, which gives you access to the "plus.softbank" APN, however it is not possible to add LTE to this contract. Therefore, the only way to get LTE with an unlocked phone on Softbank is by getting a phone from Softbank that already connects to their LTE network. In my case, I had an iPhone 5, and this article will discuss using the iPhone 5 SIM and APN settings on the N5 (it also applies for the iPhone 5S or 5C).
1. Take the nano SIM out of your iPhone. Make sure you are signed out of iMessage first, if you were using that; otherwise your SMS's will go to iMessage and you won't be able to pick them up on your Nexus 5. You will also need a nano-SIM to micro-SIM adapter, which you can get from Amazon or in Akihabara. Pop the SIM into the Nexus 5 using the adapter.
The phone will prompt you to reboot in order to access the mobile network. I was surprised about this, as with most of my other phones, it has been possible to "hot-swap" the SIMs without a reboot.
After the reboot, go to Settings / More / Mobile Networks, and first uncheck the "Data enabled" setting (I always do this to avoid connecting to some horrendously expensive APN by mistake while setting up the phone). Then select "Network Operators", and you should see the list above. Choose Softbank this first time. After that, select the "Choose Automatically" setting to avoid getting an annoying notification every time you lose the Softbank signal in the subway etc.
Next, still in the "Mobile Network Settings" menu list, select "Access Point Names". You will see an APN named "Application" with the address "plus.acs.jp". This is the Softbank APN for SIM-free 3G phones. DO NOT use this APN. Touch the APN name to edit the details, then select the overflow 3-dot menu from the top right, and DELETE the APN. You do not want or need this APN on your phone. Back in the APN list, which should now be blank, touch the "+" button at the top of the screen, and you will be taken to the "Edit Access Point" screen for a new, blank APN. Fill in the details for the Softbank iPhone 5 4G LTE APN as shown in the screenshot above (please do not ask me for the password, as I will not be publishing it on this blog. However I am sure you can find it for yourself).
In the lower half of the APN settings, set the authentication type to "PAP", and set the Bearer to "LTE". Also set the APN type to "default,supl,mms" to make this APN your default connection for all data transmission.
From the 3-dot menu, select "Save", and go back to the APN list. Select your new APN with the radio button beside it. Go back one menu and check "Data Enabled".
If all has gone well, you should now be connected to the iPhone 5 LTE access point, and be able to enjoy Softbank's blazing fast 4G speeds!