My son's landline can no longer call my cell! It rings and rings on his end - nothing on mine!

There is apparently a call routing issue on your number, which may be limited to your son's provider or could be more wide ranging.  Who is your son's landline provider?

Can you receive calls from other people?

If you can receive calls from other AT&T Wireless customers, then your account/line/hone is probably okay.

If you can receive calls from other providers' customers (other than your sons) then the problem is likely with that provider.

I would have your son try to contact his provider and describe the problem, preferably with the additional information that other people can call you (if that's true).

I don't know the landline provider for my son, but why would he be able to call me every day since he's lived there ( 5 years) up to Monday morning? We've never had this issue before.

why would he be able to call me every day since he's lived there

I don't know.  That's why I asked you the questions I did, to try to determine what the issue is.  The telephone network is operated by dozens of different companies that have to route calls between them and sometimes this information gets updated incorrectly.   If your phone isn't getting any incoming calls, that's an issue with your routing within AT&T.  If your phone can take calls from other AT&T wireless customers, then your phone/line is okay.  If your phone can take calls from Verizon, but not (e.g.) Frontier, then (e.g.) Frontier has a routing issue that may be specific to your number (or similar numbers).

Hi cnickel3, we understand how important it is to get calls from your family! We want to get to the root cause of your call concern!

Thank you to our ACE JefferMC, for promptly replying and asking relevant questions to start us off in the right direction. 

We'll need some additional info: 

1. Have you checked that you aren't blocking calls. Change to your device make and model to get personalized steps to confirm calls aren't blocked. 
2. Do you have the AT&T ActiveArmor app, check that the app isn't blocking the landline calls. You can also set your call protection preferences. 
3. What is your device make and model? So we can provide personalized steps. 
4. Has your son talked to his provider? The concern may be on their end. 

We also recommed our troubleshooting & resolve tool to diagnose your call concern. You'll need to navigate to Fix my wireless>Connection>Phone calls or sign in to get personalized help. 

Let us know if this helps! Thank you for reaching out to AT&T Community Forums!

Rhoda, AT&T Community Specialist 

Thank you for responding.  I checked my phone, inside and out, just to be sure I hadn't inadvertently blocked my son.  I didn't. I also re-booted by phone. Today, Wednesday, I actually received a call from his phone. He said the first attempt said "all circuits are busy". When he dialed the second time, it worked.  It just seems really odd that for 2 days out of 5 years, he would hear my phone ringing and/or go to voicemail.  My phone, however, did not ring. In all the years I've had AT&T, this is the first time this has happened.

Yesterday I refreshed my phone per the ATT website.  This morning I received a call from my son.  MAYBE the issue was corrected.

That sounds great, cnickel3. If you still run into any issues with receiving calls, please do not hesitate to reach back out us. We'll be here to offer you our expert assistance. Thanks again for reaching out to AT&T Community Forums!

Nelson, AT&T Community Specialist