If I recall correctly, the SMS permission is so that the app can read the code that facebook sends to your phone to confirm that you own the number that you're

If I recall correctly, the SMS permission is so that the app can read the code that facebook sends to your phone to confirm that you own the number that you're trying to link to your facebook account. Another app that I know of that does this is TextSecure, to register your number with their servers, but then again that's a text messaging app, so I'd expect it to be reading my text messages.