CAP Kobun and Tarbosan, Capcom announced on their mobile site that they intend to release a cell phone version of Rockman X4 on December 1st in Japan. The game will be released for Docomo FOMA905i and 705i series phones.
For the most part, the game is a port of the original PlayStation version; however, only X will be playable. The port carries the subtitle of "X Version", so it would seem a separate version starring Zero will be released at a later date.
Rockman X4: X Version will run you 525 Yen (about $6.55). Very little doubt you'll see this one stateside, I'm afraid. Gotta admit, I grow jealous over all the lovely Rockman games on mobile phones in Japan. Is it simply too much to ask for something along these lines to make it to my side of the pond?
Source: CAP Kobun, Tarbosan