I have read other posts of this happening...the Nokia Lumia 521 will display the name/number of the caller but the phone will make no audible noise. In the previous post, T-Mobile's solution was to reset the phone, then provided the customer with a new phone. I don't believe this is a singled out case of the problem. Here is my experience...
My wife has had the 521 since Jan 2013 and this problem did not begin until Dec 2013. I bought the 521 in Nov 2013 and noticed my phone doing the same in Jan 2014. In both cases, the phone rings as it should some times, but occasionally the name/number shows but no audible noise occurs. I thought my wife was just mistaken at first. Maybe her ringer was off or so quiet she didn't hear it, until it started happening to my phone.
Here are the steps we've taken/noticed to troubleshoot the problem...
1. Reset phones.
2. Changed ring tones.
3. Turned on/off vibrate.
4. Calls from T-Mobile users as well as other service providers are missed.
5. Happens when we are home with 4 bars as well as at the store with 2 bars.
6. Text messages and phone calls are affected.
7. I regularly plug headphones/aux cable into my phone. My wife does not.
For T-Mobile service representatives, my wife does not have a warranty for the phone, but I have a Geek Squad, full coverage warranty on my phone.
For other 521 owners, have you experienced similar problems? The last post I read on this issue included alarms being affected but I have not experienced any issues with my alarm not going off in the morning (that I've noticed, I set 3 alarms to go off every morning just minutes apart).
Maybe there is some magical solution for to this...any suggestions?