For those of you that are having the problem with MMS for iPhone you can use this tutorial to restore your MMS.
iPhone iOS 4.0 Jailbreak tutorial Windows 7
To Jailbreak iPhone 3G, and 3Gs (4G coming soon) and iPod Touch 2G, and 3G with the newest firmware you need to…
1) Update to the newest iTunes.
2) download redsn0w_windows
Here is the MAC OSX version of redsnow
3) download restore ipsw firmware for your iPhone or iPod
4) Run RedSnow and follow the on screen instructions
a) Run Redsnow
b) Choose the firmware you downloaded for your iPhone or iPod. The file is probably located in the Downloads folder.
c) Click next
d) Choose the options you want then click next
e) Put the iPhone or iPod in DFU mode
f) Hold down power button for 3 seconds
g) Without releasing the Power button, hold down the Home button for 10 seconds.
h) Release the power button but keep holding the home button.
Allow the software to install then you’re done.
Open Cydia to update and fix the white Cydia icon.
After using the Jailbreak for a week I had to turn multitasking off on the 3G iPhone. It was just making the 3G iPhone lag and unresponsive.
If you’re have the same problem you should restore and rejailbreak with multitasking off. It will make the 3G respond a lot faster.
I edited the tutorial to fix the MMS problems with iPhone jailbreak. You have to do this even to fix the MMS on non jailbreak iPhones.