Phones you can go contract, or prepaid. But prepaid, I'm not sure they should even be qualified as phones so we'll just get to contracts. Contracts you will pay a monthly service, and a rate per min, as well as for downloading, using internet and emails. Basically.
I've been with AU, Softbank, and Docomo.
AU I got when I was a student and you can get a gaku wari, half off your service plan. So it can work out cheap if you don't use it much. Back then every student was on AU for the discount, so you call all your student friends cheaper and do short messages to them.
Softbank you can get a cheaper montly rate if you sign up with them for two years. But despite being on their gold plan I always rang up a huge huge bill somehow. Keitai internet I suspect, despite being on their internet packet... They've just done a 'white plan' which is like 1000something yen a month...but I suspect if you go into 'normal' japanese usage the bill will pile up with that.
And Docomo, well I know alot about this since I just brought a new phone with them this week. Bad thing, you need to BUY the phone even if you're signing up with a new contract...and well I wanted the new P904 series with all the bells and whistles, so yeah that was pricey.
They have various levels of plan you can go on, like how much it costs per mins. The bigger your level the cheaper it is to make calls.
But Docomo I think really can't compare with all the little services you can pay extra for (why YES of course I needed to have the scrolling news/whether/sports/horoscopes updates on my phone!)
And they have this 2-1 service which means you can get 2 numbers and 2 email addresses, which is handy if you want say QueenDom.I-love-S&
[email protected] for uh friends, and
[email protected] for work.
Also docomo has internet packets, which like the phone rates are the higher level you are on, the cheaper it is per byte of internet you download. BUT, they have a 'all you can use' packet, which means you can download games, music, look at the whether forcast all you want.
Oh and Docomo has a few discounts. They have a yearly discount, it starts at 23% discount and goes up every year or something. And a family discount/singles discount...
Also the advantage with docomo is that it's pretty popular so most other people are on it.
Yes this is all very complicated and I'm sure there's more I signed for than I realised.
So for me personally, I'm taken with Docomo's phones and services, and the all you can use for the i-mode services (internet, email).
I'm pretty sure the major phone companies all have english websites, just google them.