MMS issues since at least FR11 with some SIM cards

[Guest conceptics]

The problem:

Can't send MMS. While sending a MMS, the mms remains in status "sending" for a couple of minutes without anything happening. This is regardless of network protocol (3G, 2G, Edge or H).

Receiving MMS works, Internet using mobile network works fine as well. APN settings seem correct and should be correct accoarding to my mobile network provider (Sunrise in Switzerland).

This used to work flawless on the stock LG firmware. I'm not 100% sure, but I think it also used to work on FR10. It hasn't worked on FR11, FR12, FR15, FR16beta3 so far.

Since having this problem, I also tried switching to another SIM card of a different provider to see what happens. Using a SIM card of provider Swisscom, MMS receiving and sending works fine. While doing this test, I used my Sunrise SIM card on two other phones and on those, MMS sending and receiving works perfectly.

Could there be an issue with Modaco using some SIM cards only?

@Paul: If you can look into this, that'd be great. Is there anything I can provide you with to help reconstuct the issue? Logs?

There's a MMS debug in the LG hiddenmenu, though activating that doesn't really make much difference....

[Guest conceptics]

Just to add btw:

To try to solve this issue, I have tried both the Google-SMS/MMS and LG-SMS/MMS app. I have also tried a 3rd party app, like handcent without any difference at all.

Any help, suggestions or ideas would be appreciated.