I believe that the Facebook Application stores some phone numbers in my phone book as +1(908)5551234.
As a result when I send text messages to these numbers they will send, but not be received. For example… when I get a text from my wife the top of the text screen will say +1(908)555-1234. If I were to immediately reply to her then she will not get the text. But if exit out of the text screen, and reopen her text, then the number will not have the +1 prefix and the text will send and be received a-ok.
Droid 2 unrooted