Asterisk SIP user vs peer

Asterisk SIP 'users' and 'peers' are have been the source of much confusion for Asterisk users.

With newer versions of Asterisk the concept of SIP 'users' will be phased out.

Quotes from Kevin Fleming of Digium on Asterisk Mailing list Dec 23, 2005:

As of Asterisk 1.2, there is no reason to actually use 'user' entries
any more at all; you can use 'type=peer' for everything and the behavior
will be much more consistent.

All configuration options supported under 'type=user' are also
supported under 'type=peer'.

The difference between friend and peer is the same as defining _both_ a
user and peer, since that is what 'type=friend' does internally.

The only benefit of type=user is when you _want_ to match on username
regardless of IP the calls originate from. If the peer is registering to
you, you don't need it. If they are on a fixed IP, you don't need it.
'type=peer' is _never_ matched on username for incoming calls, only
matched on IP address/port number (unless you use insecure=port or higher).