You may want to try resetting your network settings, and verifying that 3G is enabled (instead of being just on Edge).
Here are a few things to try in-turn (aka just one of them might work)
Reset Network Settings: Go to Settings > General > [scroll down] Reset > Rest Network Settings
Reset All Settings. Go to Settings > General > [scroll down] Reset > Rest All Settings
Restore your iPhone using iTunes, and set it up as a new iPhone instead of restoring the back up.
Check if you have new carrier settings available. Go to Settings > General > About to check.
Find the MMS settings for your Carrier on Google, and set them up in Settings > General > Network > Cellular Data Network > MMS
I found this list on ithinkdiff.com, but I'm new to the forum so I can't post links yet
