Custom Alert for Internal Calls

I am fairly new to this PBX system. I have a client that would like a different Alert for internal calls to extensions. I have spoken with my phone company and they told me to place an alert from the phone into the PBX Alert info box in the inbound route. Well I tried and that was a no go. I have read through numerous articles on this website and just tried updating the alert info with with the <> at the ends. However I will not find out till tomorrow if that will work. I am running version 2.11 of the free PBX. According to that post you don’t need to change anything on that phone. The phones i have are Grandstream GXP 2100. I have found that there is the pbx config file (extensions_additional.conf)and i am hoping that i won’t have to change or add anything in that. If anyone can shine some light on this i would be very grateful.

Thank you