Incoming caller ID

I have recently inherited (yesterday and not by choice) a system using PBX Firmware 1.817.210.58-1

We have customers on it one of which has 3 incoming DID’s. The incoming caller ID works on DID 2 and DID 3 (they all rollover) but not on DID 1 which is his main number. I know we are getting the information passed to us but I am not sure where to even begin looking for the incoming settings in the web interface.
I would greatly appreciate any help as I stumble through a steep learning curve.

Also what is the best document to download and read over the weekend that will give me a basic working knowledge of the system?

On the customers end we are using a Grandstream GXW-4004 V1.5A and connecting the lines into a TalkSwitch 480VS, using application version 7.11.004.

Thanks

System Sum-up
CentOS 5.8
FreePBX 2.10.1.2 firmware 1.817.210.58-1
Intel Xenos 3.6

Are these number on an IP Trunk? I assume they are. Have a look in under “Trunks” first of all to find out which trunk these calls are coming in on. The have a look at “Inbound Routes” and you should see entries for each DDI number as passed to your system by your ITSP.

What do you means by “rollover”? Do you mean they divert elsewhere?

In terms of reading you could do worse than start by looking at the docs here: http://www.freepbx.org/support/documentation