Nice site! I did a similar trick to what Richard explained above for people with a mobile phone on the Vodafone Ireland network using their e-merge service.
I call my own mobile number and leave a voicemail - I then have e-mail forwarding of voicemail setup, which delivers any message received from myself to to my blogsite, which then uses a perl script to process the message and blog it. Tout simple... ;-)
Here's a test comment...