To nico-chan:
The 6,930 for Plan M is the base rate, which does not take the applicable discounts into account.
If you look at the discount services page that lists all the potential (monthly) discounts:
http://www.au.kddi.com/english/charge_discount/discount/index.htmlThe discount that applies to everybody is the so-called My Plan.
http://www.au.kddi.com/english/charge_discount/discount/personal_discount/index.htmlwhich takes off 36.5% of your monthly bill, but requires a 2-year contract with a 9,975 early-termination fee.
I think you mentioned that you will be a student during your one-year stay in Japan.
If that's the case, you qualify for the Student Discount
http://www.au.kddi.com/english/charge_discount/discount/student/index.htmlgives you 50% off your monthly bill and has a one-year contract with a 3,150--an all-around better deal. It cannot be used in combination with My Plan.
There are other plans/discounts that may be applied to your monthly bill.
You can see that you don't really get as many free minutes as you do in say, the U.S. for about the same amount of money. Going over will of course incur call charges.
Packets are basically bandwidth (internet usage) charges you incur when you use internet services with you phone. That includes send e-mail(au's C Mail service), surfing the net, download ringtones and games, etc. The basic (elective?) charge for the EZ WIN plan is
300, and you get charge per "packet," or you can sign up for any of the fixed-rate packet discount plans. It costs .2 per email. The good (or bad, it depends) thing about it is that your "free minutes" allowance can apply to your packet charges as well. So you run less of a risk of going over on packets if you use the internet services more than you call.
Be careful, though--using the internet with your cellphone can be very addictive. Sky-high packet charges may result.
So you have:
Base rate - applicable discount + EZ WIN charge (elective?) + packet plan charge (elective) + call & packet overage charges + misc. fees (surcharges, etc)
And that, is but the tip of the iceberg...