Twitterific was the very first app that I downloaded when I got my new iPhone 3G. It's a great toolset for keeping up with your Twitter friends when you're away from your computer and out and about in the world.

Twitterific (iTunes link), by Iconfactory, does all the basic stuff you'd expect a Twitter client to do. You can read messages from your tweeps (that's what we Twitter-elite types call our Twitter friends), post messages of your own, and get alerted to private direct messages and public @replies.

But Twitterific for the iPhone goes a few steps further. It taps into the iPhone's built-in location services. With your permission, it will let your tweeps know where you are, and let you know when your tweeps are posting from nearby.

Twitter users often use the service to post links to interesting Web content, and Twitterific for the iPhone has its own built-in minibrowser to view those links. That's an important feature because third-party iPhone apps -- including Twitterific -- are not allowed to run in the background, so if you switch to the iPhone's built-in Mobile Safari browser to view a link in Twitterific, the iPhone shuts down Twitterific and you have to re-start the app when you return, which takes a few seconds. Because Twitterific has its own built-in minibrowser, when you're done looking at a page you can shut the browser and return to Twitterific without interruption.

Twitterific also lets you upload photos directly to the TwitPic service, and then link to them from your Twitter account. However, I had trouble getting that feature to work right -- it uploaded my photo sideways. Apparently, this is a long-standing bug. People on Twitter are commenting on it.

Twitterific comes in two versions: A free, ad-supported version and Twitterific Premium, (iTunes link) priced at $9.99. The Premium version doesn't have ads, and you can change the background to a light color. I don't think there's any need for most users to upgrade to the Premium version: I found the ads on the free version to be completely nonintrusive and, while I didn't care for the dark background, it wasn't that big a deal. However, I upgraded Twitterific to the Premium version anyway, just to show appreciation for a job well done.

I've tried a couple of dozen iPhone apps, and Twitterific has the best user interface of the bunch by far. Every little detail is devoted to making it easier to use, and to maximizing effectiveness of the limited real estate available on the iPhone screen. The icons are self-explanatory and the minibrowser, in particular, is a lovely way of allowing people to check Web pages from Twitter without interrupting the experience. The first time you use a feature of Twitterific, you get a page of tips on how to use it. Every iPhone application designer should be looking at Twitterific to see how it should be done.

As good as Twitterific is, I want more. I'd like the ability to create groups of users, and have a separate screen for viewing @replies and DMs, and integrated Twitter Search.

More free iPhone software:

Google Mobile App Streamlines Search

UrbanSpoon Is A Fun Way To Find Local Restaurants

Zenbe Lets You Make Checklists