I have added two features that allow talk to be used over AX.25, with 
the ax25d daemon, or possibly with axl (although I haven't tried that).

First, if the stdin is not a tty, line-mode is used instead of curses.
This makes talk appropriate to use with the ax25d daemon.

Second, if the first argument starts with plus (+), the rest of the
first argument is an alias (or a callsign).  This is ignored unless the
user is packet.  But if the user is packet, the alias is used instead of 
packet for registry with talkd.  That means the alias, or callsign, will 
show up in the message that says somebody wants to talk to you.
The username "packet" can be changed in the Makefile.

I cannot claim that this program is perfect or even safe. 
Use it at your own risk.  

Here is the line I added to my ax25d.conf file:
default         * *    *   *   *   0    packet    /usr/bin/talk talk +%u dcb
(the 'dcb' is my username.  Yours will probably differ.)

--
Dave Brown N2RJT
dcb@vectorbd.com
April 25, 1996