It works like this:

- start twibble
- start GPS and wait until it says GPS in the title
- go to ‘Update Profile Location’
-  select ‘Geocode and update’

If everything works well you should see your location in your twitter profile settings. (Source: Twibble blog)

More about Twibble:

twibble mobile is a twitter client for the Nokia N95 and other Java enabled smartphones. Its feature list include

    * post messages via your mobile network (WiFi, UMTS, GPRS), or using text messages (SMS).
    * auto refresh: twibble can retrieve tweets automatically after a given time period.
    * optimized to generate as little data traffic as possible. Only new tweets are fetched to reduce data traffic.
    * integrated timeline: Tweets and direct messages are displayed in a single list sorted by date. There is no need to retrieve tweets and direct messages separatly, or to switch between various lists.
    * open web links contained in a tweet (via phone browser).
    * re-tweet (forward) of tweets.With a few clicks you can re-send a tweet you received without re-typing.
    * quick @replies
    * you can add friends
    * mark tweets as favourites: Useful on the road when you want to mark a tweet for later reading.
    * cancel network requests (twibble is multi threaded)

In addtion twibble mobile can add your position to a tweet (but only if you want!). It can even make use of the built-in GPS of the N95 or other GPS phones. The position can be displayed on the mobile device and on the desktop in Google maps or Google Earth,

See http://www.twibble.de/twibble-mobile/

to get Twibble Mobile jump to  http://m.twibble.de and download the software