With Twitter now reaching the mainstream, we thought we'd look at several of the most popular iPhone Twitter clients.

If you're new to Twitter, it's a messaging tool that allows you to broadcast short notes (called "tweets") to your online followers and to follow messages sent by other people. Sign up for an account here (http://twitter.com) and then follow this writer's Twitter feed (http://twitter.com/TDreier).

Twitterific comes in free and premium versions. Both offer a simple interface that lets you view tweets as they come in. Twitterrific Premium ($9.99, available here) lets you view messages in black text with a white background, while the free version only shows white text on a black background, which is harder to see. The premium version is also ad-free, while the free version shows a small ad for each 50 messages.

The app is loaded with helpful hints to help you get the most out of the features, and it allow for sending direct messages, re-tweeting a message (forwarding a twitter message with your own comments), and sending a Twit Pic (you can choose a photo from your library or take a new one).

The downside here is, naturally, the price. While it has stronger features than other free Twitter apps we've seen, there are lower-cost apps that match Twitterrific Premium's features. We'll explore another of them next week.