Welcome, First you must know what is Asterisk and what is it used for:
[quote]Asterisk is an open source framework for building communications applications. Asterisk turns an ordinary computer into a communications server.
You can use Asterisk to build communications applications, things like business phone systems (also known as PBXs), call distributors, VoIP gateways and conference bridges. Asterisk includes both low and high-level components that significantly simplify the process of building these complex applications.[/quote]
You can’t build a CRM using Asterisk, You use Asterisk to do Telephony Integration with your CRM.
If what you want is built your Asterisk GUI. Take a look to the FreePBX source code