Update: SwirlyMMS 1.2 official is now available from the Ste repo in Cydia! No need for the procedure below...
I got the new version of SwirlyMMS that works on 2.0 and 2.1 firmware (as well the iPhone 3G). Its a beta version and maybe we will have the final throught the AppStore. SwirlyMMS its the only application that allows you to send and receive real MMS and it doesnt use some internet service over WiFi
* Download this file: test.list
* SSH the test.list file into your iPhone in this root: /etc/apt/sources.list.d/
* Open Cydia and wait for a refresh of Sources.
* Now click on the Changes tab and there will be SwirlyMMS
Note*: You can find some carrier MMS settings here