Originally Posted by JTG
Strangely enough, being an undocumented/illegal alian does not preclude one from getting a social security card or driver license in the US. At least not in California. So there would be no difficulty in flying, within US borders for these folks.
I know SS cards are available to those who don't have residence here. If you're going to be doing financial transactions (ie, open a bank account etc) you need the number anyway. I have seen a SS card that says "not valid for employment" that was issued to a person in such a situation.