i need help

[gabdarb]

I have 4 cisco cp-7841 phone and i want them to work like intercom like I can make calls between them and be able to call 911. I'm trying to be cheap because it's not a business i don't want to buy an 800 phone big system for big corp. I'm trying to be really cheap. What can I do to just make them work. i also have freepbx

[Brendan Ord]

If you convert the phones to the MPP firmware you will be able to access a web interface and register the phones to your FreePBX system.
You should also be able to customise some softkeys to take advantage of the intercom or paging features of FreePBX (sorry, it's been a hot minute since I've used FreePBX/Asterisk).

If the phone PID (on the box, or back of phone) contains 3PCC, you do not need to convert the firmware and you're good to go.  If not, it is using Enterprise firmware and will need to be converted.  Here is a link with details:
Convert Cisco 7800 and 8800 series IP phones between Enterprise and MPP Firmware - Cisco

Best of luck!