Saturday, July 30, 2011

Do discounts make your mobile bill more expensive?

This morning, I went thorough one year's worth of Docomo bills and reverse engineered the number of minutes I talk each month. The reason for doing this is so I can decide if the b-mobile Talking FAIR SIM would be a good deal for me and my family. I did something similar for my data usage before moving to a data-only FAIR SIM, but have been avoiding doing the same thing for voice, simply because of the complicated nature of Japanese mobile invoices.

Part of what makes it complicated is the way discounts are applied. The full, undiscounted charge first appears before all or part is subtracted. Neither the price per minute nor the number of minutes used is reported (unless you pay extra). To figure out how many minutes I am using, I had to sum the pre-discounted prices for all the different call types, and then find the exact cost per minute (¥42) for my plan from Docomo's website.

(¥3,800 + ¥260 + ¥40 + ¥420) / (¥21/30s)*2 = 108 minutes

As I was doing this, I realized that I am paying for "discount" services that cost me money, specifically the "yu-yu call discount" (ゆうゆうコール割引).

This allows you to register 5 domestic number for discounted calling - 30% off for Docomo numbers, 10% of other carriers. However, the service costs ¥180 per month. For the discount to be effective requires at least 15 minutes per month in the case of a Docomo number, 45 minutes for another carrier's number, or some combination of the two.

It turns out that I don't call enough to warrant the yu-yu plan. In the image above, I was only discounted ¥82. Over the past 12 months, I paid an additional ¥2,340 but only was only discounted ¥1000 in return. So, it actually cost me ¥1340. That's not a lot - ¥100 a month, but a hundred yen is a hundred yen. There was only one month when the math actually worked out in my favor. Guess how much money I saved.

Four. Whole. Yen.

Yeah, lemme go cancel that today, two days before the start of the August billing cycle.

The family plan on the other hand is definitely saving me money.


  1. Yes thats how it is with all you can use plans (and all you can eat buffets !!) it voice, data or food. We overestimate our capacity to consume!!

    With Softbank White plan, I dont think I make enough "free" calls to justify the 980 yen per month. Probably I will be better off with NTT VOIP service for 315yen/month along with Fair data. If I can get wife to shift too, it will automatically be free calls between us 24x7.

  2. Yes, thats right. Even with the CyanogenMod 7.1 RC-1 (based on 2.3.4) on my DHD, if I use the native SIP feature in Call Receiving mode, battery does not last the whole day. However with "Outgoing only" option, it lasts as much as it would without SIP.

    Ofcourse, there would be other considerations like VOIP quality over 3G, since it seems that G729 (which is good for 3G) is still not supported by native SIP or most of the free voip apps.

  3. ht03a→atrix tokyoAugust 4, 2011 at 11:05 PM

    and forever docomo we will be...