Unlocked iPhone 4 help?

[betty]

So I just unlocked an AT&T iPhone to be able to use for tmobile. The only problem I have encountered is that I'm not able to receive nor send pictures or mms messages to people who don't have iMessage (so regular text message people)
Someone told me there is a separate app for that but I can't find it?

What can I do?

[Elizabeth]

You shouldnt need another app but there is one try pinger. Will you click on my pic and go to my profile so i can get advice frim other people about my question tere is inlynlike 3 questions please??

[Eve]

go to settings, then scroll down till you see messaging select it then it will say imessage then you can turn it off or on to use it. mine was like that too but it works after i did that.