Seeing as twitter seems to have stopped accepting my sms tweets without a PIN even though one isn’t set up I went in search of a simple twitter client for my phone.  The first one I found was twibble which so far is working very well and supports both tweeting via 3G/GPRS/WIFI on the phone as well as sending them via sms if you want.  Twibble also has support for using twitpic to tweet pictures.