[clintjm]

If you want to avoid the Iphone for whatever reason, Symbian OS based S60 and up are good choices. Motorola Razrs V3 or better are good choices as well. Both can be loaded Japanese language packs and both have apps for learning.

3g WCDMA 2100Mhz phones that are unlocked will work in Japan with a prepaid softbank sim if you actually wanted to take your phone over there.

PalmOS and Windows based phones are also nice choices.
I used a palm pilot PDA for years with learning apps and dictionaries

You don't have to break the bank to buy a Iphone or Japanese electric dictionary to have pocket power nor be tied to online contracts.

Not really what you asked about but some alternatives.