There are two ways to use Twitter.  However, using Twitter on your phone to update your status is the point of the service.  Not everyone has unlimited text messaging, if that is your case, you may want to use your cell phone's mobile browser to update your status without incurring text messaging fees.

Depending on your phone, you want to open up your mobile browser. As long as you have it enabled on your phone, this should be easy to do. Once opened, you want to navigate to m.twitter.com. That is the mobile site for Twitter. It is a bare minimum web site that is meant to run on a mobile browser. It will show you the barebones of your Twitter account page, you will want to log in to view your tweets and followers.

Once logged in, you can update in a box similar to how you would if you were updating from the web at your computer at home. You still only have 140 characters to utilize, so be as brief as you would normally be. You send the tweet once you are finished, and it will go out to your followers and post to your Twitter profile page. It is just like using Twitter.com normally.

Twitter really was meant to be used on a cell phone via texting, but if you cannot use texting or run out of texts during the month, using your phone's mobile browser as an alternative.  Only use Twitter this way if you have a data plan on your phone or you may incur additional fees.  Take the time to research that before you use Twitter this way first.  This will keep everyone up to date on what you are doing while you are on the go.  Take advantage of Twitter in any way possible, whether it is on your phone via texting or mobile browsing.