Genlemen–thank you for your help. I believe I’ve had a bit of a breakthrough after both of your suggestions.
I now am able to get a distinctive ring on the phones using the Alert Info: <aitchteeteepeecolon//127.0.0.1>; info=priority
Strangely enough, I’m unable to edit the base file for the phone configs
Per Grandstream’s documentation P1488 = priority and P1489 = 1 should yield a Custom Ringtone 2 on Alert Text ‘priority’.
When you actually change the settings manually and export the device configuration, you can see that the P1488/1489 flags are being modified–however, when I change the base file and rebuild config and update my phones through FreePBX, the change is not being made within the headset after reboot. I’ve got several other custom basefile modifications that continue to work just fine. It’s possible I need to report a bug.