I wrote about mobile manga earlier, now the article MANGA ON THE MOVE, Cellphone Comics Are Latest Commuter Pastime (May 30, 2006), offers some of the secrets of success:

Apart from the ever-increasing range of titles, two main factors appear to be behind the comics' success. One is their low prices of around ¥40 to ¥60 (40¢ to 60¢) per story, which makes them quite a bargain. The other is convenience. Readers can download only those comics that they want to read, as opposed to paying for a whole magazine with numerous comic strips in it. Not only that, but readers of electronic comics need not deal with the burden of carrying around bulky magazines.

When the comics were first offered, most were aimed at men, particularly office workers who commute on public transportation. But the number of female readers has since grown rapidly, now that reading from mobile phones is considered cool. In response, publishers are working on providing female-oriented comics for mobile-phone subscribers. This development may provide an additional boost to the market - from men who are fans of girls' comics but would be embarrassed to be seen buying such magazines in stores.

See also:
Quicktime Movie from 2005 about Mobile Manga
Quicktime Movie from 2004 about Mobile Manga