Talking Caller ID doesn’t Talk

Switched from a cordless phone to a corded phone for my GWES PBX phone extention (fed from a GrandStream HT801 ATA), and I was given a little talking Caller-ID device. It clearly recognizes the Caller-ID burst, but I guess since its only a four-digit number (that’s the length of our extentions, and this system has no PSTN access) it doesn’t auto-read.