MCI Address
 When you ask to add a new address (or person to send a
 message to), you'll be asked to specify what type of address
 you want:

                  +----- Address Type -----+
                  |  MCI Instant           |
                  |  Paper Mail            |
                  |  FAX                   |
                  |  Telex                 |
                  |  External Mail System  |
                  +------------------------+

MCI Instant
  If you're sending a message to another MCI subscriber,
  choose this item.

Paper Mail
  Paper Mail will be printed a the MCI center nearest to where
  you want the mail sent.  You'll need to supply a full
  address, but the recipient need not be an MCI subscriber.

FAX
  MCI can send your message to any FAX machine.

Telex
  Allows you to send your messages to a Telex machine.  You
  can also receive Telex messages.  Your Telex number is 650
  plus your MCI ID.  For example, if your MCI ID number is
  111-2222, your telex number would be 6501112222.

EMS (External Mail System)
  Allows you to send to other mail systems, such as
  CompuServe.