In the previous post, I described the effect of variable monthly usage on the total, longterm cost of a data plan. To keep things simple, I considered only one person (me) using one device (my phone). The outcome was that both the 5 GB and 2 GB plans (coming soon from Docomo) would be less expensive for me than just continuing to use my current 7 GB plan. There was a good chance that the 2 GB would offer the most savings, but only by a very modest amount of a few thousand yen over 2 years if I don’t modify my future behavior to minimize the number of times I would exceeding the 2 GB quota.
This result is really not surprising and could be obtained without all the extra work of a Monte Carlo simulation, but it was a good way to introduce the framework. Now, I’ll expand it to consider more sources of variance (i.e., more devices). For now I’ll continue to keep it simple and consider just two devices, so the result will again be a bit obvious. (For the next post on this topic, I’ll consider multiple people sharing a large family data plan, the results of which will be much more difficult to predict without simulation.)
Current data plansLike the previous example, this post will also consider my real usage. I currently have two active SIM cards, one voice+data and one data-only:
The FAIR data plan is the most expensive offered by b-mobile, but it is the only one that has the same average speed and latency as a standard docomo plan. The 1 GB is good for 4 months, so it is ideally suited for devices that consume only 250 MB per month. Of course there are much cheaper ways to get this small amount of monthly data, but speed and responsiveness are hugely sacrificed. (See here for a series of posts on the b-mobile FAIR SIM)
- 7 GB Docomo Xi Flat rate (¥5,700/month)
- 1 GB b-mobile FAIR (¥7,953/4 months)
The above probability density functions (PDFs) show how I expect my phone (right) and tablet (left) to consume data in the future. The b-mobile FAIR SIM uses around 250 MB per month, often a bit less, so you can probably already imagine, based on the result outlined in my previous post, that canceling it would save money.
Data plan optionsTo keep the high speed and low latency of the FAIR SIM, I have three options:
- 7 GB Xi and b-mobile FAIR: ¥5,700+ approx. ¥2,000/month
- 2 GB Xi and additional data-only SIM: ¥3,500+
- 5 GB Xi and additional data-only SIM: ¥5,000+
The outcomeSee this new post for new results taking into account the data plan cost.
¥140,000 (Both the 2 GB and 5 GB plan split across two devices) ¥170,000 (General cost for the 2 GB or the 5 GB and the FAIR SIM (not shown) ¥185,000 (Cost of 7 GB plan and FAIR SIM — status quo)