Why can't iPhone do MMS?

ok so i just got a iphone 3g 8gb BUT i cant get any pictures and i cant send any :/ this IS a problem and i wanna fix it. oh and its unlocked and jail broken so i can use it for tmobile.

i installed mms on my iphone 2g and it was working perfectly and then i had to restore it and i jailbroke it again and installed the mms but i can recieve mms but i cant send i have tried changing the mms settings and mms proxy and all that but it still...

is there any setting i need to change or something specific i need to do to allow the photos to go through text messages the last couple of times i tried, it attempts but says ...show more

My iphone 3G is updated to the 4.2.1 software, but i still can't send pictures. Is it because i do not have the data plan?

When ever i try to update it gives this message: Itunes could not update the carrier settings on you iphone. An unknown error occured. (0xe80003D). Make sure your network connection is active. Then try agian. My internet is working and ive restarted...

i cant find mms on my iphone 4 to send photos everyone elses iphone has mms on it except for mine please help my iphone 4 is running on ios 4.2.1

My samsung infuse cant recognize mms sent from iphone but it can recognize if sent through email. It says this type of picture is not compatible with your device, so how do I fix that? My girlfriend has an iphone and i cant view any mms she sent me....