Originally Posted by jackal

Yes, you are automatically an extra driver at no cost. If you read the Terms and Conditions of the rental contract (it'll either be on the inside of a rental jacket or on the reverse of your signed paperwork), it will say something like "AUTHORIZED DRIVERS: the person named on the rental contract and his or her spouse"). Thus, you are legally able to drive the car without signing.

Note this is no longer the case with Dollar or Thrifty (they now require the spouse to be listed on as any other additional driver and now actually charge as any other additional driver), but it is for virtually everyone else, including Avis.

You will NOT be able to add anyone else to the rental contract without them being present, as the rental agency will need to take their driver's license information and have them sign the rental contract. Therefore, you cannot add them as additional drivers when you book (reserve) the vehicle, nor can you when you pick up the vehicle. You also cannot do so over the phone, since the rental agent will need to physically verify the license and will need the driver to sign. If you are renting from a corporate location or an agency location (i.e. not an independent franchise, which is exceedingly rare to encounter with Avis), you should be able to add on an additional driver at any other corporate or agency location, since they all use the same computer system. You should probably check that at the counter when renting, however.

In extreme situations, I have seen some rental agencies (usually smaller, more flexible franchises) accept a faxed driver's license and return-fax signature from the additional driver, but this is not common and is probably against corporate policy with Avis. I would not expect them to do this for you.