I had the same problem and here's how I fixed it: Go to Settings - Do Not Disturb - Allow Calls From. Check to make sure its set to Everyone. After downloading a software update my phone stopped ringing and when I checked this setting it had been set to Favorites so unless the call came from someone on my Favorites list it didn't ring. Hope this helps!
WOW guys, after struggling for months, I've finally found a solution for this problem.
Details on my situation:
I bought a T-mobile iphone 5s in Mexico that i unlocked successfully with R-sim.
My iphone is on ios8.2.
After 2 weeks of usage, i noticed my wife wouldn't respond to my texts or calls. I began to wonder, then i realized that i could send texts and realize calls with no problem but not receive them.
I struggles with Do Not Disturb, i restored my phone, i reset network settings, and waited patiently for other alternatives while researching EVERYWHERE!!!
I was starting to blame the heat, the rsim, the Telcel signal down here, and endless culprits.
I read on the most unlikely of places a tip that caught my eye.
I read something about a conflict caused by LTE, 3g, 2g and home wifi signals, which caught my eyes because i knew days before i noticed my problem i fiddled with my settings.
AMAZINGLY, when i switched Voice & Data under my cellular setting to 2G, IT WORKED!!! i receive calls, make calls, receive and send text, no internet due to the unlock but its ok.
I really hope this helps guys, i know i had special circumstances but hey, any help is useful.
I hope my post isn't removed because of my methods, but give it a try guys and let me know if it results.