>>16
First things first, Japanese phones are usually locked in all kinds of ways, and they need to be unlocked using intrusive methods if you want to use it on your foreign network.

You can either buy a Software Unlocked phone, or you can buy a Hypersim to unlock them. A Hypersim is like another thin simcard you put over your real simcard, and you can then use your phone on your gaijin network. It works with almost all models, but it's unreliable and breaks down all the time, and annoying tricks are needed to get it to work again. Would not recommend. The other way to use it on foreign networks is to buy a Software Unlocked phone. It's what it sounds like; Someone has edited the firmware to allowed it to be used on non-Japanese networks. This is the best option, as it all works just fine. In the old days only a few phones had this option, and it was expensive, but now the main companies Softbank (I would guess Sharp too) can unlock phones for you in-house, so there are a lot more choices on the market. But it costs extra.

However, note this; Almost all the special features on your new shiny phone WON'T WORK; because most is still locked to Japan despite the hypersim/software unlock. So you won't be able to use Internet, MMS, or other cool features. You will ONLY be able to call or SMS. There are a few exceptions, but assume it will be non-functional. There's a way around this crap. Sharp makes phones for Japan, but also for Taiwan and China. They're almost exactly the same phones, but the Chinese phones are always fully unlocked per default, and with functional internet, TV, etc..

Now, you can take the easy route and buy from Ebay, J-Phone.ru, or Zeroxkeitai.com. That saves you all the hassle of importing. Otherwise, buy from Japanese Yahoo or from Softbank/Sharp themselves, but assume it will cost much more. If you want a Chinese phone, use Ebay or find a reliable Taobao agent, then buy a phone from there (Taobao is Chinese Ebay, more or less). If you know what you're doing you can find a 480x854, 8megapixel flipphone for less than 300 dollars, easy.

As for models, Here are a few good Chinese versions, there are less choices compared to the Nipponese side;
SH7218U, SH0902C, WX-T930

As for Japanese versions, there are a ton of valid choices, but I would only buy the super cheap versions since they're all feature crippled anyway, like the 740sc or 707sc. But I'd like the super cool SH-10C, if I had the money, because despite it's non functional 3G internet it actually has working Wifi. Check ZeroxKeitai's site, he has the cheapest Japanese phones around.

Obviously, buying Keitais requires research and dedication, it's not as simple as checking Ebay for five minutes.