I recently bought a bmobile sim and I think it was listed as an additional 1000 or 1500yen if the staff sets it up for you. However the setup is really easy with the English guide included. I only needed a wifi to connect.
I found this,
http://www.bmobile.ne.jp/english/ and will try this out when I go there again...I use so much data there, and I wish it would be cheaper...
Notes to some of the guys from a lesson I learned...
1. Luckily my airbnb came with a mobile hotspot and used that for the data during my trip, until I hit the data limit. It seems a lot of Airbnb rooms in Tokyo provide one. Take advantage of this. Connect it to your external battery pack, so you can stay connected all day.
2. Hotspot worked great until I hit the cap... I have used hotspots in the past with bad results... Usually the hotspot and my phone would lose the connection and it was a pain in the ass... but not this time and it always stayed connected.
3. As my iPhone treated the hotspot as a regular WIFI connection, my phone behaved accordingly, sucking as much data it needed (downloading podcasts, uploading photos to icloud, updating apps, etc etc). It will be a pain, but I need to manage this better with my next trip.
4. If you want a local number, I advise to get this package at the airport and not in the City. Last time I was able to get a local number at the airport. It was pricey, 7.5K for Minutes and 3 GB data. I assumed I could get one in the city this time, and was given the run around about how it was not possible for a short term visitor. I didn't push back, wasn't worth the effort.
5. I didn't push back too much because I was able to use my phone with US number, and using Tmobile, it wasn't too expensive...Tmobile may suck at times in the States, but internationally, they standard benefits is pretty sweet.