MMS is proving to be a pain. After spending a long time configuring and setting up mbuni, I discovered that it does not offer any support for GSM modems, unless you pay extra for commercial plugins. Consequently, it will be expensive and difficult to develop a picture uploading system that operates using the built-in "send-a-picture" functionality.
However, it seems as though this might end up focusing the project a bit better. I now plan to develop a J2ME app that does uploading of pictures via a web link (rather than MMS). This app can also be extended to resize media before uploading to save bandwidth, strip metadata to improve anonymity, and even possibly provide some encryption. The app can be set up to work with moving upload targets to help maintain uplinks should the server get blacklisted. I think that focusing on an app like this could result in a more tangible and functional product than an MMS based solution that requires tricky server setups to use. The application could be improved by future developers as well.
With that in mind, I have begun development of a J2ME app. Set up of eclipse, eclipseme, and the sun wireless tool kit proved to be initially painless on linux, but then running the hello world code failed (the emulator would start then immediately exit). After a lot of pain debugging and trying to get it working on two different computers, I finally discovered the solution: when running a project for the first time, don't press the big green "Run" button in eclipse. Rather, right click on the file you wish to run, and select "Run as -> Emulated J2ME Midlet". This sets up the default launch configuration with the needed parameters, after which the big green run button should work (at least until the launch configuration changes again).