[Nexus 4 General] hammmy:
I recently visited Japan and took along my Nexus 4. The summary is, the Nexus 4 does work in Japan for data usage.

After doing some reading, I found that the Nexus 4 works with Docomo's network, W-CDMA on 2100MHz. Of course, nothing in Japan is easy, so you can't just buy a prepaid SIM and insert it--most prepaid SIMs require activation from a Japanese mobile phone. This is where b-mobile comes in--they are a MVNO reseller on Docomo's network. b-mobile sells preactivated data-only SIMs specifically for visitors.

I expected my phone data usage to be limited to web, Google Maps, and Skype for SMS and any potential voice comms. b-mobile sells two varieties of SIMs: 1GB over 2 weeks or unlimited data at 300Kbps over 2 weeks, with VoIP services blocked.

http://www.bmobile.ne.jp/english/14days.html

I chose the 1GB. Either SIM costs ¥3980 (roughly $40 now).

Initially, I planned to have the b-mobile SIM delivered to the Kansai airport's post office but as I was traveling with a native speaker, I decided to check out Yodobashi Camera (Japan's premier electronics retailer) to see what other options were available, such as this one:

http://www.yodobashi.com/日本通信-BM-FR...1GB定額-有効期間30日-標準SIMタイプ/pd/100000001001612644/

That turned out to be a bad call: Yodobashi Camera does sell prepaid SIMs but they are of the non-activated variety and the Umeda (Osaka) store location did not have W-CDMA "FOMA 3G" SIMs in stock--only the LTE SIMs. I ended up buying the b-mobile SIM online after I arrived and had it delivered to the hotel, which took two days and a third morning before the SIM auto-activated. After the SIM activates itself (two days after shipping), that begins the 2-week service period.

I used the SIM in and around Osaka, Nara, Kyoto, Kochi (Shikoku), and Tokyo. In almost every location, the service was the same: terrible. My speed tests hovered around 300Kbps up and down, only once going to 1Mbps on download outside Tokyo. I ended up using less than 250MBs of data. Unless Skype's SMS service ports would also have been blocked, I would have lost little by using the unlimited 300Kbps SIM instead--in fact, other than the alleged block on VoIP ports, I doubt very much that both SIMs aren't the same throttled service. I didn't use Skype VoIP, so I couldn't confirm whether that works. The service was also flaky, often requiring a reboot or a Airplane Mode toggle to force the connection to refresh itself and complete a request.

Overall, I was happy to be able to use my Nexus 4 in Japan. Having Google Maps available made solo navigating trivial; it even provided destination-specific train schedules with prices, although the names of the train lines reported by Google conflicted with the lines as posted at the stations: for instance, Google reported the Kyoto line through Osaka as the "JR Tokaido / Sanyo Main Line". Google's description is technically correct: Japan Rail has a main line that runs in two parts from Tokyo to Kyushu--Tokaido in the north and Sanyo in the south. However, this knowledge is assumed in Japan, so when you're standing in Osaka Station looking for the train to Himeji, you need the Kyoto line, not "Tokaido / Sanyo".

APN settings:

Name: b-mobile

APN: bmobile.ne.jp

Username: bmobile@fr

Password: bmobile

Authentication type: PAP or CHAP