There are two methods: Circuit emulation over IP, that requires certain module types, and Voice over Ip, that require other ones. I recommed VoIP as it it more flexible and bandwidth efficient.
In both cases you would use ISR router, but while with VoIP a 2801 would be enough, with Circuit Emulation over IP you would need a minimum of 2811 because the form factor of the module is network module.
there is a lot of documentation on CCO, the thing is if you never have done any VoIP design, you would probably find very confusing. I suggest you contact a reputable cisco partner/reseller and tell you want to connecte two ISDN PBX using 2801 "voice bundle" and the VWIC-1MFT-T1. If not unsure about the solution they propose you, came back here and ask again.
I have done a similar set up , so i have a router connected to the PBX at both the end with NM-CEM-4TE1 modules and below is the configuration that i applied. but my cem interface is not coming up, can some one verify my config and updated me.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...