EMobile have done quite well to make their pricing plans relatively simple, but there are still quite a few different options to consider and things to catch you out. Luckily I've had enough hours study of phone pricing plans service options to have a Phd. in the field. Here's the shortest summary I could produce that should help most people make a decision. (I haven't explained the 'whys' as that would take much longer. Here goes ...
If want voice services or want the the S11HT (Emonster) or H11T you pay a minimum of 2000 yen a month (unless you pay an extra 24,000 for the phone from day 1 in which case you'll pay 1000 yen). When you exceed 23,825 packets the cost will increase, topping off at 4,980 for data. Voice calls will cost you 18.9 yen/30 seconds. (If you pay an extra 980 yen/month calls to emobile are free, to other mobiles 9.45 and 5.25 to land lines for 30 seconds). The only reason to go for this plan is if you want one of the above devices or if you also want to use voice in addition to data. Note you can use both above devices as wired modems with the same flat rate. The S11HT can also be used as a Bluetooth modem.
If you don't want voice and don't want one of the above devices you have about 3 data plan options, but if you plan to use a lot of data, just for the the 5,980 yen a month (which is reduced to 4,980) if you sign a one year contract. You have a choice of the EM-ONE PDA, a PC card/CF card/Express card or USB modem. Only the USB and PC card support 7.2Mbps.
The above services only work when you are in an EMobile service area. You will be able to roam onto the DoCoMo network, but there's two catches. 1) The S11HT doesn't roam onto the DoCoMo network. 2) Even when you do roam with the H11T (which will be anytime - even in areas of Tokyo - when you are not covered by eMobile) you don't get flat rate data and the voice calls are more expensive.
As an aside, note you can also get 10Mbps eAccess ADSL broadband for 1,500 yen a month. If you are on the second option above it is 0 yen. So if you are already paying for broadband and can live with a meagre 10Mbps you can wipe out your home broadband costs.
For myself, I currently have two devices - DoCoMo for voice and Willcom for data. I think I'll drop Willcom and move to EMobile. I'm happy to take questions in the comments.
