We are migrating to Cisco Phones and we are told we need CER licenses for some locations

Do you have a centralized PRI or SIP trunk? Or do you have PSTN connectivity at each branch office?

PSTN

It's been my experience that if you have PSTN connectivity at each branch, you can route those calls out that branch's Voice Gateway and the proper outbound caller ID/ANI should be sent to the PSAP. Then the proper ALI should be populated to the PSAP as well. Where I've seen CER used is when there are multiple satellite branches going back through a centralized Voice Gateway.

Licensing
Cisco Emergency Responder user licenses are required for all types of devices capable of placing emergency calls, including wired IP phones, wireless IP phones, software telephony clients, and analog gateway foreign-exchange-station (FXS) ports.

http://www.cisco.com/c/en/us/products/collateral/unified-communications/emergency-responder/data_sheet_c78-711007.html

He probably means that if you have some sites from where 911 calls won't be tracked, you don't need licenses for those devices.

Are you wanting to be notified internally of these calls? I'm saying that if you are just worried about the PSAP getting the correct information and you have PSTN connectivity at each branch, you don't necessarily need CER, but if you want 911 calls to be tracked internally, you may. Or you can look at Informacast Advanced Notification as well.

No, mainly concerned with requirements and having 911 setup right and when my vendor says some sites need and some don't a red flag goes up.