Does Docomo offer 3G SIMs?

I live in Japan but was on vacation in Australia when I bought a Nokia 3G phone there. I notice that I can roam on both SoftBank and NTT Docomo's networks, but Docomo's seems to be 3.5G, whereas Softbank is just 3G.
Anyone know if Docomo allows prepaid 3G data access? If not, how much is SoftBank's? I really only want data access to check gmail, facebook, etc, on the train and don't really care about voice calls. Not sure if data-only is possible, but that would be ideal.

Neither company offers prepaid 3g data. Docomo doesn't sell prepaid service at all, and softbank's prepaid sims don't include data except for mail (some softbank prepaid handsets also support tethering which is what they refer to as data communications)

http://mb.softbank.jp/en/prepaid_service/

Thanks, Yellow Smurf. I don't suppose anyone can recommend a 3G data provider? I would be willing to consider a contract if prepaid isn't available, just depends on the price and term length. I'm only in Japan for another 18 months, so I don't want to enter into SoftBank's 2 year contracts since they apparently don't prorate the cancellation fee.

Some of the other 3G data providers I've googled seem to be selling thumbdrives for laptop data access, not SIMs for phones. Not quite sure what the secret Japanese phrase is to describe what I'm seeking, but I had a lengthy phone conversation with Docomo's english help department and I'm pretty sure the girl didn't fully understand what I want.

Unfortunately Japanese carriers generally do not sell stand alone sim cards, neither for data nor voice. There really aren't many options if you are not getting a phone from the carrier themselves. What kind of phone do you have though? If its an iphone a docomo subsidiary supposedly has a special plan for unlocked iphones. It may require a contract, although I'm not sure of the details. It was mentioned in an iphone thread earlier this year.