After seeing the 5 GB cap for "unlimited" usage on Docomo's Xi LTE data plan, I went through the past year's cellular bills to figure out how much data I was using and how I would be potentially effected if I started having to meter my data usage.
The answer, with a caveat, is not at all. Over the last year, I have used on average 250 MB of data per month. If you recall, I rooted my phone in April. Prior to that, I average only 130 MB per month. Since then, more like 360 MB. But, I am admittedly not a heavy user of data. I really don't stream much of anything. The most data intensive app I use is Google Maps, which I do use quite a lot. Since rooting, I do tether my notebook or iPod Touch, but not to excess, though I may do that more often now that I see that I am well under any potential red-flag-raising bandwidth consumption. (CEO Yamada said 99% of FOMA users are below 5 GB.)
Now for the caveat. If I was using Xi, I'd have a more powerful handset that could tame that CPU hog Skype, which is worthless on my older handset. I'd also be more apt to browse more pages simply due to the higher speed of the handset and the connection.
As far as streaming content, last I checked, none of the free streaming music apps allowed Japanese IPs, and if someone surreptitiously removed the youtube app from my phone, it might take me several months to notice, if ever.
So, Let's make some assumptions about my future usage. First lets assume that my data usage doubles, which would mean that I'd be using about 0.7 GB per month, still well under the cap. Next let's add in 30 minutes a day of skype, which is assuming a lot. Let's assign a rate of 200 kbps for skype usage.
200 kb/s streamed for half an hour = 0.0429 GB * 30 days = 1.29 GB per month.
Adding this to my doubled usage gets results in 2 GB per month. I'd still be at only 3.3 GB per month if I used skype for an hour a day.
Finally let's assume I am so enamored with the video capabilities of my new dual-core handset that I am streaming video encoded at 500 kbps, also for 30 minutes a day.
500 kb/s streamed for half an hour = 0.107 GB. * 30 days = 3.22 GB per month.
So, for me, doubled usage, plus 30 minutes of skype and 30 minutes of streaming video would put me just over 5 GB.
How would this work out for the rest of you?
(Granted, the idea of making every phone call over a cellular data network through skype is appealing, but the call quality I get with skype just doesn't quite cut it.)