Hi
I do not recommend to install 3CX when you have CRM. We have clients that had it and ended up with the IIS configuration for 3CX being compromised by CRM and other applications.
For example - in this scenario HTTP compression may go on - This will break IVR.
The Websites might have rights changed. We have seen cases like this. modification of read/write access on our web applications.
Even an update needed for CRM will modify settings in the .net framework - this will break 3CX Web section.
If you are going to try this Make sure you use 3CX version 7.1.
Also you can use Cassini - this is a standalone application that works separately from IIS- it is a strip-down of IIS and lightweight. This is why we package Cassini as well - for these type of scenarios.
Alternatively you can keep 3CX separately on a virtual machine. This will also be a good solution and install it using any webserver you want. Just to give you an idea if you have 2000 calls a day, a server 2003 installation with 1GB of Ram on a good host of course will be enough.