So, like the other Dave, I've run into some unfortunate side effects of using a Cisco 26xx router.

I'm running IOS c2600-ipvoice-mz 12.3(9) so thankfully I've got support for the
? ? x25 route (...)(...).. xot dns \2.\1.x25.org
line in the config and my router is able to lookup other hosts.
I did have to configure the access-list to allow all IPs, otherwise it was rejecting all XOT traffic incoming and outgoing.

I have managed to set up a config where analog calls to WIC-2AM modems get presented a hidden menu that resembles the prompt you would get when connecting to TELENET/DATAPAC/TYMNET.
This allows you to connect to a short list of up to 17 predefined hosts (18 menu entries max, including the exit command).

Where I've hit a stumbling block is having a way to map incoming x25 calls to give remote access to my analog modems.
It would appear that "interface Async<x>" doesn't support "encapsulation x25" on the c2620 which as I understand would be needed for it to work how I want.

For now I guess I can use the cisco for outbound calls to a limited subset of TELEBAHN hosts. I'll have to figure out how to get inbound x25 calls routed to a modem bank hanging off another box eventually.
I'm sure someone has a better idea for this, and I'll probably replace the hidden menu on the c2620 with routing through something running on a linux box eventually.

-DK

relevant lines for the dial-in menu:

!
modemcap entry AUTOANSWER:MSC=S0=1:TPL=default
modemcap entry NOANSWER:MSC=S0=0:TPL=default
!
alias exec tpcbbs pad 78398001
!
menu tpcnet prompt '@'
menu tpcnet command 783980 tpcbbs
menu tpcnet command tpcbbs tpcbbs
menu tpcnet command exit exit
menu tpcnet default exit
menu tpcnet line-mode
menu tpcnet single-space
!
banner motd '

TPCNET
783 235 0$(line)A
'
!
line con 0
no motd-banner
!
line 1 4
exec-timeout 0 0
x25 subaddress line
vacant-message ''
modem Dialin
modem autoconfigure type AUTOANSWER
autocommand menu tpcnet
no activation-character
length 0
transport output pad telnet
autoselect timeout 1
autohangup
stopbits 1
speed 115200
flowcontrol hardware
!

?

So, like the other Dave, I've run into some unfortunate side effects of using a Cisco 26xx router.

I'm running IOS c2600-ipvoice-mz 12.3(9) so thankfully I've got support for the
? ? x25 route (...)(...).. xot dns \2.\1.x25.org
line in the config and my router is able to lookup other hosts.
I did have to configure the access-list to allow all IPs, otherwise it was rejecting all XOT traffic incoming and outgoing.

I have managed to set up a config where analog calls to WIC-2AM modems get presented a hidden menu that resembles the prompt you would get when connecting to TELENET/DATAPAC/TYMNET.
This allows you to connect to a short list of up to 17 predefined hosts (18 menu entries max, including the exit command).

Where I've hit a stumbling block is having a way to map incoming x25 calls to give remote access to my analog modems.
It would appear that "interface Async<x>" doesn't support "encapsulation x25" on the c2620 which as I understand would be needed for it to work how I want.

For now I guess I can use the cisco for outbound calls to a limited subset of TELEBAHN hosts. I'll have to figure out how to get inbound x25 calls routed to a modem bank hanging off another box eventually.
I'm sure someone has a better idea for this, and I'll probably replace the hidden menu on the c2620 with routing through something running on a linux box eventually.

-DK

relevant lines for the dial-in menu:

!
modemcap entry AUTOANSWER:MSC=S0=1:TPL=default
modemcap entry NOANSWER:MSC=S0=0:TPL=default
!
alias exec tpcbbs pad 78398001
!
menu tpcnet prompt '@'
menu tpcnet command 783980 tpcbbs
menu tpcnet command tpcbbs tpcbbs
menu tpcnet command exit exit
menu tpcnet default exit
menu tpcnet line-mode
menu tpcnet single-space
!
banner motd '

TPCNET
783 235 0$(line)A
'
!
line con 0
no motd-banner
!
line 1 4
exec-timeout 0 0
x25 subaddress line
vacant-message ''
modem Dialin
modem autoconfigure type AUTOANSWER
autocommand menu tpcnet
no activation-character
length 0
transport output pad telnet
autoselect timeout 1
autohangup
stopbits 1
speed 115200
flowcontrol hardware
!

?

This is what it has currently grown to. The menu 'tpcnet' is what is presented to dial-up modem clients, so there is no menu text, just an @ prompt, as you would get from the likes of TELENET/DATAPAC/TYMNET services back when those were operating still. You had to know the host address you were connecting to, or its mnemonic for well known services. One difference is due to the limited nature of the cisco menus, I've left out the "C " at the beginning. Maybe I'll make an actual shell at some point and offload the menu system to a linux box.
I also added two other x25 routes to handle single digit subaddresses, as well as a default subaddress of 99 since that seems to be the de-facto rotary everyone is using as their main entry point.

I do have a rotary working now to the modems.
78323589 -> modem pool, currently the PBX is offline, so no dialtone. with the PBX online (and all the cables plugged in) you would be able to dial numbers in the 980-xxxx exchange and connect to other modems hanging off the PBX.

The full config minus sensitive bits and voip stuff (my C2620 is really a VG200 that has had the boot rom swapped out to unlock its full capabilities):

!
! global parameters for all PAD connected lines