HTC's Twitter client, Peep, does not automatically shorten URLs. ShortenMobile is a small background program that watches the clipboard of the device and automatically shortens the URLs for you.
Currently implemented url shortening services:
How to use:
* Install the cab file
* Open ShortenMobile from StartMenu
* Activate the checkbox "Run at startup"
* Click on Hide-Softkey
* Copy any url (including "http://" at the beginning) to the clipboard
* The shortened url is available in the clipboard after the confirmation dialog has been shown
[Via Pocket Now]