There is also not an app for turning your car into a spaceship.
(If I lost you here, it's because what you are asking can't be done)
If you believe this can't be done, you're wrong. Apple won't allow it. I would love this feature. I'm not giving up my iPhone because of it, but it seems to me this feature should have been implemented when imessage was developed.
And for all you people saying "go get an android then", you need to realize that's it's perfectly normal to have a device you like and still criticize certain aspects of its operation. AND it's ok to be critical of Apple. I know some of you can't fathom that....