There are at least 2-3 different native iPhone Twitter clients out there, and none of them are as interesting as Twinkle.

In short, Twinkle – the unofficial Twitter client for your jailbroked iPhone (that’s a mouth full) adds third party location meta data and photo sharing to your Twitter tweets. It also allows you to look for tweets by other (that are near by) with the same or similar location meta data.

Privacy note: the location meta data are submit to third party Twitter developer Tweetscan, and not officially part of Twitter, so just be aware of that…

The original Twitter has the concept of “location” “L:” as a short-hand for tagging location, but nobody really use it since it’s a pain to enter that by hand. Twinkle solves that problem by hooking into iPhone’s location api (?) and automatically generates that as you create your “Twinkle Tweets”.
With the “enhanced Twinkle Tweets”, you can look for the tweets that are physically around you, say, 5 miles from where you live or work. As an example, I’ve found a few twitters that are in my town (about 20 miles away from San Francisco) that are also testing out Twinkle – these are people I would not be able to look up in the past or would not have bordered with.

For extra credit, you can also attach photo (taken with your iPhone’s camera) to the Twinkle Tweets. To me, it’s like real-time Flickr photo sharing with people within your area. Again, another reminder, the photos are send to Tweetscan / Twinkle and not Twitter.
As I am writing this, Twitter is giving me 403, blank page, etc. Twinkle as a service that piggy back on top of Twitter of course had stopped working. >.>;
This whole “thing” is rather new, and there’s some serious potential… We will see how things are going to go another year from now….