People who have used the iphone have had the trouble of being harassed by imessage ads, and now the new ios system comes with the function of filtering unknown senders, teach everyone how to set up
Go to the iphone4s system desktop and tap Settings
Select information in Settings
Look for the option to filter unknown senders in the message and turn it on
Also in the information Settings, select the Blacklist option as marked in the picture.
Click on the Add option to add people you don't want to receive messages from.
Experience for reference only, I hope to help you.