sometimes you just have to create a new GPRS APN for fMMS, and to do that you can install fAPN from extra-devel (if i'm not mistaken)

i've tried setting fmms without creating another GPRS APN because my phone operator has the same setting for both GPRS and MMS, but fmms didn't work...

so i tried creating a new GPRS APN & do the correct setting according to my phone operator and fmms works just fine

hope this helps