Exotel is cloud based telephony system i.e all of Exotel data is available over the web. This makes it cross-linkable with other cloud based applications easily such as CRM, ERP, CMS etc. There are 3 broad classifications of API implementations :-
1) Incoming Calls/SMS via Passthru
-> The Passthru Applet makes an HTTP GET request onto a URL(on your server) with the details of the call. Every call accumulates data as the call progresses. For e.g in the beginning of the call, the only data available is "From Number","Time of Call" & "Call SID". As the call progresses, more information gets added to this call such as "To Number","End Time","Duration","Recording URL". The fundamental principle of these integrations is to be able to pass on the Call details onto your CRM to make an Auto-Entry. You can also use the "Agent Passthrough" to identify which agent is getting the call if the implementation involves popping-up the details of the customer on your CRM page.
2) Call API
-> The Call API is an HTTP based REST API which allows you to trigger an outbound call using a button on your internal application. You can make use of the "Status Callback" to auto update the details once the call has completed. You can even use the Call API to trigger IVR calls(calls from machine to human) and ask for a set of responses.
3) SMS API
-> The SMS API is also an HTTP based REST API which allows you to trigger SMSes using actions/buttons at your internal application.
A combination of these 3 will give you extensive integration between Exotel and your CRM application. As the APIs are HTTP REST based, Exotel can be integrated with ANY cloud based application.