Why won't my iphone 4s send or receive pictures?

I have an unlocked iphone 4s that I use with T-mobile. I know that it is not a problem with T-mobile as I was able to send and receive pictures a few days ago before I switched to an iphone. I've read a few different things online saying that its a problem with iOS 6 but how do I fix this? Step by step instructions would be appreciated as I'm new to the iphone

Call T-Mobile and figure out with them why their network isn't complying with your phone.

Go to settings, messages, and make sure mms is turned on, and if so toggle it on and off. Also reset your network settings. So there must be some sort of setting issue nothing more than that.

Turn on cellular data in settings

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