Or rather, i think when i send an MMS via handcent, one is sent by the stock messaging app also. I send a lot of MMS, and this is beginning to annoy people. There has got to be a solution...
yes. go into the stock messaging app, click menu then settings, then notification settings. uncheck notifications. go into handcent and do the same except make sure that notification IS checked. you will only receive a notification for handcent.
Are you rooted? I had this issue. You have to go to the system folder with root explorer or something similar and either rename or delete mms.apk. Or you could freeze it with titanium.