Finally got round to test fMMS ver. 0.3.1 (as a follow up to my previous test of ver. 0.2.8). Here's what I've got:

• Sorted out APNs on device, basically I have deleted "T-Mobile MMS" profile and added proxy address to main "T-Mobile Internet" profile, leaving "Use proxy" tickbox unchecked. That way same APN profile serves for general internet browsing as well as sending/receiving MMS.
• Sending MMS to wife's SonyEricsson S500i stripped text again with that weird "Text fMMSpart6306 was deleted due to: no legal rules found for this media (-1)" message.
• However, sending MMS to self (both send & receive via fMMS) did NOT cause stripping text, while fMMS ver. 0.2.8 did that, as per previous test.
• Auto-receiving messages works like a charm! Both from self, as well as wife's SE. But condition is that I'm manually connected via GPRS/3G, of course - otherwise fMMS tries to open MMS forever...
• Odd "AAAA" button is gone from received messages, which is great plus.
• Sent messages don't display my avatar in the list. Avatars are only displayed at received messages.
• Usability note: would it be possible to sort "Open file" list while adding attachment by date / newest first? It's quite inconvenient to scroll all the way down to reach the latest picture taken by camera.