If you got an alert in your Samsung Galaxy S2 that say: message may be corrupted on recipient device. Do not send the message because your friend will get a ???? text message. Follow this tutorial to fix the problem.
Step 1: In the Attention message click Cancel. This will not send your message which is good for now.
Step 2: Go to Messaging app.
Step 3: Click Settings.
Step 4: Click Input mode.
Step 5: Select Automatic.
It should send message with regular text instead of ??? text.