Twitter client for Pocket PC. Uses the m.twitter.com inside the browser, but has notifications and I think it has all the basic needs to twit on your Pocket PC.

PocketTweets is a Web-based Twitter client for the Apple iPhone. See the latest tweets from your contacts, update your status remotely, or see what's happening around the world by viewing the public timeline. -- all via EDGE or WiFi.

Moby Picture allows you to send pictures from you mobile phone via MMS and it can automatically be sent to your twitter account.

"Abiro Jitter (Java Twitter) is an easy-to-use and fully-featured Twitter client for mobile phones.

Benefits compared to using SMS to communicate with Twitter:

Less expensive than SMS (and especially so if you have a flatrate subscription), as information is sent over the data connection
Notifications don`t fill up your SMS Inbox
Support for more languages (actually any, provided the phone supports them)
More functionality, e.g. listing of timelines and users, as well as direct messages
More responsive
Jitter communicates directly with the Twitter server, increasing performance and reliability."

"Hahlo is an iPhone-styled interface for the great Twitter service, and it is built upon their simple API.

All you need to use Hahlo is a twitter account. Your login details are not stored by hahlo.com, they are saved in a cookie to allow access to things such as your direct messages, and enable you to update your status directly from hahlo."

Twitteresce allows you to access your twitter feed using your mobile phone. All you need is a twitter account, a Java J2ME enabled mobile!