after change the carrier.... can still online?

hi all i have jb to v3.1 on my 3gs... and my maxis is 5.0, now cannot sent mms, izzit fine if i reset my network setting? if after i reset do i need to do any setting back for the network to work? how to make it turn back to maxis 4.0?

Edit: what I know is at for my phone the carrier need to be 4.0 but after jb to 3.1 the carrier change to 5.0, so if I reset the network setting so will the carrier change to 4.0? Or is there anyway to do it?

This post has been edited by wayne78: Oct 11 2009, 01:06 AM