Got an unusual one for you. I have 2 digital single line phones (in classrooms) that won't ring when called. The caller hears RNA. The phones are not in DND. Tried swapping out phones. No luck. For the heck of it, I plugged in a 22 button display phone in its place and tested. I could see who was calling in the display,and it did ring kinda sorta however, the ring tone was something unusual, can't explain that. The speaker and handset work fine. Any thoughts? Sounds like some feature was activated, but don't know what.

perhaps the ring tone was set to something the DSL's can't accommodate.

From user guide:
To change your extension’s incoming ring tones:
1. Press idle CALL key.
2. Dial 820.
3. Dial 1 to set Intercom ring; 2 to set trunk ring.
4. Dial code for the desired ring pattern:
1 High pitch
2 Medium pitch
3 Low pitch
5. Press SPK to hang up.
To listen to the incoming ring choices:
1. Press idle CALL key.
2. Dial 811.
3. Dial 1 to listen to Intercom ring; 2 to listen to trunk ring.
For trunk ring, enter the tone you want to listen to followed by the tenant group.
4. Dial code for the ring pattern you want to hear.
1 High pitch
2 Medium pitch
3 Low pitch
5. Press SPK to hang up.

I'll give it a try when I go back this afternoon. Gotta admit, I'm starting to think its a hardware issue though. They called and said 2 more phones are acting up. Thats 2 on one card and 2 on another in less than a week. I'm bringing some cards and a cabinet with me just in case.

820 was the magic number. I changed the ring tone and voila, it worked. I am still puzzled that the single lines wouldn't ring when the tone was changed. That's what threw me. I was beginning to think it was hardware. Anyway, that won't happen again, I deleted 820 from programming.