Skype (owned by eBay) is a great way to study Japanese. Skype is instant messaging software (like AOL Instant Messenger or Yahoo! Messenger), but it also lets you make phone calls and do video chat. It's also popular worldwide.
But, though you can use Skype to call real phones from your computer (handy if you're in Japan or if you have friends in Japan-- I use it myself to call home for $0.02/minute), the real highlight is that you can make computer to computer calls free. All you need is a microphone or headset, which you can purchase cheaply at most electronics stores (or is already built in if you have an Apple Mac).
Skype isn't the most popular way to IM in Japan-- it doesn't compare at all to cell phones-- but there are many users, and there are many other students from other countries studying Japanese. So, if you want to search for a language partner, with a little luck you can find someone and have an excellent exchange.
If you're interested, you can reach me on Skype under the name:
mr.kaeru
Talk to you soon!