[Long story short, someone added a completely unnecessary Docomo APN to Cyanogen's APN list. This list is used by many ROM developers. The APN was added ABOVE the proper flat-rate APN causing this unnecessary APN to be the default when flashing for may users (perhaps those flashing after a full wipe?). Sending of just one packet on this unnecessary APN would result in the 4200 yen charge. (What are the chances of a background packet being sent in the time it takes to navigate to "Access point names" in settings after first booting a new ROM?) This "bug" in cyanogen's list persisted for 2 weeks until Takuro Kurame aka northeye found and fixed it. The bug was fixed prior to the start of the November billing cycle but the existence of the bug was not publicized in English or Japanese, so people who flashed CM6.1rc1 or any ROM using the buggy APN list got charged an extra 4200 yen for November. The bug persists in CM6.1rc1 which should be avoided by Docomo users. Ok maybe this wasn't very short.]
UPDATE: It seems that I'm not the only one hit with a charge. Please leave a comment with information on your tethering and voip habits. If you could specifically answer the following questions, it would be helpful to all. I am trying to figure out if Skype is in fact going to a problem to use, or is Docomo has started policing for tethering, or if some of us just got unlucky.
1) Have you ever tethered?
2) Have you ever used skype?
3) Have you ever used another voip client?
4) Have you even been charged 4200 yen extra for tethering?
5) If so, when were you first charged?
6) During the billing months prior to being charged had you ever used skype?
7) During the billing months prior to being charged had you ever used another voip client?
Skype for android was introduced in early October. Prior to October billing, I had never heard of ANYONE being charged for tethering. Of course there is also fring and SIPdroid, but perhaps since they are less well known, their usage doesn't raise flags (?)
Probably not, but I'll need to hear from you to confirm. Has anyone who has been using skype last month been assesed a tethering charge by Docomo?
I just got hit with one on my October bill. I used a total of 511.31 MB - up a whopping 25.69 MB from September. The charge was an additional 4200 yen that I was told could be incurred for two reasons 1) not using the unlimited biz-houdai APN* or 2) tethering. Docomo broke down my packet usage and assigned about 175 MB to my phone and the remainder to tethering.
Fortunately, Docomo just adds a flat fee on top of your bill for tethering, which is not even in violation of the terms of service - just imagine my bill if they would have charged me the standard packet rate for the remaining 330+ megs (like softbank has been known to do).
Of course I was tethering last month and had been this month, as well (until I got the bill at least), but Docomo has confirmed that there are no tethering charges on my bill for this month. So what gives? If they caught me last month, why did they stop looking at my packets this month? Either I was unlucky last month, Docomo was looking more closely, or I did something to attract attention.
What did I do differently? Nothing I can think of other than attempt a call over 3G with the skype android app at the beginning of the month. I didn't realize at the time, but skype (and all VoIP usage) is banned on the FOMA network.
Could it be that the skype usage flagged me and triggered inspection of my subsequent packet headers? Who knows, maybe it's just karma - after all, I did recently write a post on my data usage and tethering.
This actually has me reconsidering my perspective on data caps. It is conceivable that with a 5 GB cap, any usage will be allowed, since bandwidth is bandwidth, nothing more nothing less. But with an unlimited data plan, the carriers obviously have a very good incentive to keep PCs off their mobile networks. For my personal usage, I don't even come close to 5 GB. In fact, I haven't even exceeded 0.5 GB (last month was 0.499 GB).
So part of me feels it is ridiculous to be slapped with a tethering charge for using half a gig when people can easily chew up
* I was previously told at a different Docomo shop that connecting to the wrong APN will actually result in no flat rate whatsoever and a very expensive bill.