Although the device is market as a router, it is actually a low end smart phone, with infrastructure mode WiFi tethering pre-configured.  In fach, the first thing you see when you turn it on is a giant "Pocket WiFi S" button on the main screen.  If you press this, the tethering turns on, and you can access the device from other computers (phones, etc.).  The fact that eMobile markets this device as a router rather than a smart phone probably has to do with the fact that it's a very low end smart phone, and users who planned to run a lot of apps on it might end up dissatisfied.  

The data plan, though, is eMobile's smart phone plan, not their computer plan.  (The SIM cards are different colors, too).  In fact, if you ask eMobile, they'll tell you that any and all of their phones can be used for tethering, just by plugging them into the computer.  That's great!  Softbank, NTT Docomo, and other carriers charge a "basic" fee, usually 2000 yen to 4000 yen per month, then charge per minute for outgoing phone calls, and then charge yet more for data (f.e. 4000 yen per month for the unlimited iPhone data plan).

With eMobile, the basic fee is the data fee, so it's certainly a better deal than the other carriers provide.  Their basic plan is around 4000 yen per month base fee, which is possibly more than some of the other carriers charge, but since it includes data, it is certainly less than the other carriers charge for base + data.  As with all japanese carriers there are no voice minutes included, and the per-minute rate is not all that competitive.  eMobile does have a promotional plan, where one can spend a small monthly fee and get a large number of minutes free, but you have to sign up before the promotion is over.  

So, you get cheap phone calls if you want, or don't pay for phone calls if you don't want to use it as a phone.  You get a nice WiFi router that can also accept incoming calls for free, and happens to have the benefit of being a low end android device as well.  The price per month is about the same with the regular Pocket WiFi service (if you don't buy the voice plan), and.. the Pocket WiFi S unit itself is actually cheaper then the original Pocket Wifi!

Sounds great, right?

Sure, except for two things...

1. The speed is not as fast as the original Pocket WiFi - Although the rated speed is the same, various tests show that it simply isn't as fast.  Perhaps android is weighing down the processor.  Perhaps the WiFi or 3G chipset is not up to par.  Perhaps the antenna isn't very good - we don't know.  What we do know is that the Pocket WiFi consistently outperforms it.  The difference isn't huge, but it's noticeable on larger files. 

2. There is a bandwidth cap - it's mentioned in the fine print of the contract.  Once you go over 350 megabytes or so in a day, they begin throttling the speed of smart phone SIM cards.  It's not dial-up speed or anything, but it's nowhere near 7.2Mbps either.

Number 2 is especially noticeable because unlike U.S. carriers, eMobile doesn't cap or throttle their normal 3G data service at all.   We frequently download things like XCode, Linux disk images, etc., over both HTTP and BitTorrent with no problems.  I can download TV shows and Movies from iTunes Music store, system updates from Apple and Microsoft, etc. with no issues either.  Obviously, if you have a daily limit of less than 400MB, you won't be getting too many TV shows downloaded. 

On the other hand, if you want to be able to browse some web pages, check your mail, etc., then around 350MB should be more than enough.

So what's the conclusion?

If you need 3G internet for relatively light use, then it's fine.  If you want to combine your phone and internet bills, it's great!  If you want 3G for heavy use (i.e. for your main connection), it's not good.  If you are a heavy user and want wireless, go for the original Pocket WiFi.  If you want faster 3G and wireless isn't important to you, eMobile also offers 21Mbps and 42Mbps speeds now in USB form factors.

One final consideration - apparently the Pocket WiFi S is unlocked, which means that one could insert SIM cards from NTT Docomo, or a data SIM from eMobile and use those, without the bandwidth limitation.  (Of course you probably won't be able to make phone calls directly on the Data SIM, you would have to use Skype or such).  The APN settings will likely have to be changed in order for this to work.  

In fact, we've done some testing for you:

Note that getting the data connection working requires modifying the APN settings.

Another interesting thing to note is that if you are using this device as a portable router all day long, the battery life may not live up to your needs.  Although you can connect it to USB to charge it, if that isn't possible, you can also consider the extended battery pack from MUGEN POWER. (Search Amazon Japan).