On Saturday 26 Nov 2011, Shamit Verma wrote:
Just like other countries with national IDs handle this issue. Till you are a visitor, your visa or TAX ID serves as ID. Once you get resident status you get national ID like SSN.
SSN is just that: needed for social security. If you're Gill Bates, you don't need an SSN since it's unlikely you'll ever be on the dole. It's not mandatory.
Regards,
-- Raj