Great job to the developer - this has been MUCH needed by the iPhone community! It will be interesting to see how MMS receiving is implemented here.
MMS is available via installer.app (You need to add http://modmyifone.com/installer.xml to your source list to get it)
or download the files now from here. Unzip, copy files to /Applications/MMS.app/ and chmod +x mms.
NOTE: this is still an early beta release. It is slightly buggy, but is apparently working.
So far I have not managed to get it to send on the Vodafone Network here in New Zealand, but others have reported this as not working yet (so more of a Pre-Alpha relesae then?)
The interface is quite good and lets you view a thumbnail of the image before selecting it. I noticed the save button when you enter the settings doesn't seem to do much, but when you have entered the info required use the arrow at the top to go back and the settings stay there.
Also Note: You need to have GPRS working on the iPhone and Wi-Fi turned off?? I have posted the settings below you need for this to work. As yet I have had no success in sending, if anyone does please let me know (and yes I have contacted Vodafone and asked them to enable MMS on my account.
GPRS/EDGE Settings
APN address: live.vodafone.com
Username: blank
Password: blank
MMS settings
MMSC: http://pxt.vodafone.net.nz/pxtsend
Proxy: 172.030.038.003:8080