To get started, you need to connect your iPhone to your computer. Once your iPhone is connected, iTunes will open. You’ll see a message saying that an update to your carrier settings is available.
Select Download and Update.
The new carrier settings will download quickly; it shouldn’t take more than 30 seconds. You’ll see a progress bar running while the download is underway. Do not disconnect your iPhone while it’s running.
When the download is complete, you’ll see a message telling you that your carrier settings were updated successfully. Then, your iPhone will sync and backup as it normally does when it’s connected to iTunes. Let this process run.
When the sync is complete, you’ll see a message that it’s okay to disconnect your iPhone. Go ahead and do so.
Now you need to reboot your iPhone. You do this by pressing and holding the power button (you’ll find it on the top of your iPhone, on the right side). On the screen, you’ll see a message that says “slide to power off.” Do so.
Once your iPhone is completely powered down, restart it by pressing the power button again.
Now, MMS should be enabled.
Go back into the messaging app: When you compose a message, you should now see a camera icon underneath the body of the message. Tap that to add a picture or video to your message.
Also, when browsing photos and videos in your photo library, you should now see an option to send the photo or video by MMS. Previously, the only option for sending photos was via e-mail.
Congratulations! Your iPhone is now capable of sending and receiving picture and video messages. Enjoy.