Should I sign up for an unlimited data plan for Japanese cell phones?

If you’re like me then you want to know if it’s worth signing up for the unlimited data plans offered by Japanese keitai companies.

I use KDDI and conveniently lost my old phone somewhere between South Africa and Hong Kong, so upgraded to a smartphone when I got back to Japan. I spent awhile digging around the KDDI web site trying to figure out if it was worth signing up for their unlimited data usage plan.
In short : 
Double Teigaku Plan :  4.8MB – Unlimited    :  2,100 to 5,900 yen
IS Flat Plan        :  Unlimited            :  5,400 yen
Cost Breakdown
As I’m currently strapped for cash, I was wondering whether or not I could get away with having a smartphone and not pay the 5,000 yen/month unlimited usage plan. Given the way the representatives talk at the AU store or elsewhere, I thought there wasn’t any option but to sign up for the unlimited data usage plan. However, in AU’s case, they give you the option of signing up for the unlimited plan or the double teigaku plan.
For the double teigaku plan you pay a base cost of about 2,100 yen / month up to 5,900 yen / month. 
For the IS Flat plan you pay 5,400 yen / month. 
Bandwidth Usage
So how much bandwidth can you use with your 2,100 yen? About 4.8MB or 40,000 packets. A packet with AU is 128 bytes.  Now 4.8MB is not going to get you very far once you step out your door and stop using the WiFi in your house. Just a quick look at my inbox and I’m probably averaging 8KB to 16KB per email message.  A few of them have attachments, so one download of my inbox could easily put me up to 2MB. 50% of my monthly allowance in just one email check (caching aside).
What about surfing the internet? Just visiting this page used around 70KB and I have little in terms of images or fancy graphics. ESPN’s top page? Anywhere from 250KB to 2MB. Two visits to ESPN and you’re done surfing for the month.
Of course, you could keep surfing and the beauty of the Double Teigaku plan is that you can’t use more than 5,900 yen / month, but that’s higher than the IS Flat plan to begin with. If you planned on using just a little bit more, then you’re looking at about 500 yen / 1MB of data usage.
Those who want a smartphone so they can carry their schedule, todo lists, contact lists, etc around with them and not pay the hefty data usage plans, signing up for the Double Teigaku plan is worth it.
If you plan on using Google Maps, navigator, facebook, and other online interfacing apps, then just go for the unlimited plan.
What’s your experience? Softbank or Docomo users out there must have similar plans. Would be interested in hearing about those.



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