I have been using an excellent piece of software for twittering form my Windows Mobile. Twikini has all of the features you would expect, as well as working fantastically with the IPhone like features of Windows Mobile 6.5.
I had used a few of the other apps that are available, but I think this is the best for the way that I use Twitter. The only thing that I have had a problem with is that on my phone keyboard between the “r” and the “t” is the hotkey for “Tweet”, and I quite often send in an unfinished tweet. Really a phone issue, but could do with an optional “confirm tweet” checkbox.
Ahh well, can’t have everything…