If your employees use a CRM system for handling incoming and making outgoing calls, then in order to integrate the Gateway with CRM it is enough that your PBX supports the function of connecting external numbers (was not locked to use one service provider), or it had the ability to connect another external SIP connector.
Our Gateway for Telegram calls successfully works with such systems as Bitrix24, AMO CRM, Retail CRM, SalesForce CRM, Pipedrive CRM and many others. In most cases, the integration is done through a plug-in module for SIP telephony (virtual PBX).
Some CRM systems, such as Bitrix24, support the connection of additional external SIP connectors (besides the main PBX). In this case you can connect the gateway as an external SIP-connector, regardless of what PBX is used and whether it supports the ability to connect external lines, which are also called trunk (VoIP Trunk).
Usually when configuring the gateway used registration option PBX->SIP.TG
(the bot gets details to connect to the gateway and they are specified in the settings PBX). Most popular virtual PBX (onlinepbx, uis, etc.) and office PBX (Asterisk, Panasonic, Oktell, FreeSWITCH, SipXecs, Yate, FreePBX, etc.) provide this option.