IPhone 3GS doesn't tell me when the message has been read by the receiver?

I think I might have missed the update. If you think that's what happened would you mind telling me how to receive this update?

If you are using iMessage, you will only be told if the message has been read if they enable the setting on their phone. They have to allow you to see that they have seen the message. On the phone you are messaging, go to Settings>Messages>Send Read Receipts (Enable it)

You also have to have iMessage enabled, which should be just above it.
Hope I helped!