I did enough research on reading RFID tags using Android phones(smart phones).
My understanding of this is that for NFC-enabled smart phones (Nexus S) it is possible to read RFID tags, but there are restrictions.
For non-NFC-enabled Androids we need a RFID reader to which we can communicate from Android using Bluetooth.
My question is:
Please, check the on-line Android documentation for an answer to the first question.