Echofon has its own URL scheme. You can add a bookmarklet to Safari to post a link with Echofon. Add the following URL to the bookmarks on your Mac/PC; then sync your iPhone.

Free:

javascript:window.location='echofon:///post?'+window.location

Pro:

javascript:window.location='echofonpro:///post/username?'+window.location

For backwards compatibility, these URLs also work if you replace 'echofon' with 'twitterfon'.

Alternatively, open http://www.echofon.com/b with your iPhone and follow the directions for installing the bookmarklet.

Note: Make sure turn on JavaScript on Safari. You can check it in Settings.app.