Developed in open-source fashion by @sugree (93,216 tweets so far, as of 2008.01.13), jibjib* is a Twitter client designed for Twitter-addicted on-the-road.
50 KB in size, easily fits in any Java ME (J2ME) phone (CLDC 1.0 and MIDP 1.0 minimum), and still loaded with handy features like quick reply, url-friendly smart retweet, custom/auto word list for quick insertion (like @having or #gaza), and able to open url in a tweet directly. Another plus, small bandwidth consumption, via birdnest proxy (5-6 KB for 20-entries timeline).