Twittelator is a full featured Twitter client that helps you stay in touch with friends. It has a smooth UI and is easy to navigate. What makes this app stand out from the other Twitter clients is the Help button that sends out a geo location + emergency message so that you could be found. Keep in mind the GPS on the iPhone is not the most accurate so if you were in trouble it could take your friends some time to comb the area in an attempt to find you. Plus the time it takes to load the Geo location you could have twittered a detailed message to your friends instead.

Cost: Free
App Store Link
Developer Link
Twittelator Support