Don't leave MVNOs for new docomo shared data plans

More than ever, if you are looking for mobile data access for a single device that won't be used as a phone, then MVNOs in Japan are your best bet.

I realize that I greatly misinterpreted the cost of docomo's new data plan for data-only devices. I think the original materials I read didn't include mention of the "base fee" for data-only devices. (At least that's my story and I'm sticking to it. ;))

You see, there is already the ISP charge of at least ¥200, then there is the share charge of ¥500. What else can there possibly be? Where is there room left to manufacture additional charges? Unnecessary ISP charge? Check! Charge for adding an additional line? Check!

Turns out there is also the "data plan" at ¥1,700, which is to put it bluntly pretty much bullshit.

What do you get for the ¥1,700 data plan? Nothing. There is no included data allowance. It is simply the NEW base fee to enable a data connection on a tablet. If you don't add a data package, you are billed at ¥0.6 per kilobyte. The worst part is that, as far as I can tell, this "data plan" charge didn't exist before, which is part of the reason I overlooked it.

Here are the minimum costs of the new standalone data plans:

1. ¥1,700 for the data plan that includes no data.
2. ¥200 for Mopera ISP (Warning, you can't tether with a Docomo OS installed)
3. ¥3,500 for 2GB of data.

That totals ¥5,400 for just 2GB. What a horrible deal, especially when the current plan gets your 7GB for ¥6,000 including ISP charge. Conversely, the new standalone 5GB data-only plan costs ¥6,900! Why would anyone buy this?

The cost of the existing 7 GB Xi data plan for a tablet is ¥6,000.

Recalculating the potential cost of a phone and tablet

Perhaps you recall that I was considering the probability that any particular data plan would result in the lowest total cost over two years for a combined smartphone and tablet. Keep in mind that I am using the premium bmobile FAIR SIM, which has no additional speed or latency restriction, so I am paying about ¥8,000 for 1 GB of data, but since the tablet almost never consumes over 250 MB per month, this works out be a decent arrangement. The data connection is fast and responsive, unlike many of the other MVNO SIMs, and the monthly cost is about ¥2,000.

Probability Density Functions (PDFs) describing the likely future usage of my two devices.

Previously, when I used the incorrect data plan cost, the shared docomo plan was clearly cheaper. That is no longer the case. The new results are:

• 2GB plan costs less in 53% of simulations (¥182,366 ± 5887) over a 24 month period
• 5GB plan costs less in 38% of simulations (¥182,384 ± 1387) over a 24 month period
• 7GB + FAIR plan costs less in 9% of simulations (¥184,518 ± 0) over a 24 month period

Here is the corresponding result in graphic from. There is no variance in the predicted cost of the FAIR SIM because in no simulations is 1GB exceeded in a four month period.

This includes the cost of an additional Docomo SIM card for the tablet at about ¥3,000. Considering that, there is basically no difference in outcome. I'd probably save less than ¥100 per month by getting the extra docomo SIM AND I'd now be subject to a 2-year, autorenewing contract with a ¥10,000 early termination fee. The FAIR is totally prepaid.

So, unless data usage on the tablet dramatically increases, the shared docomo data plan is essentially worthless to me.