I should have reported this here months ago. But I didn't enough info to understand what was going on and where the problem came from. I'm still not really sure but maybe others do, and others have experienced this issue that no one is talking that loudly about for some reason.
But I have been suffering with this issue for over 6 months: intermittent no rings on my iPhone 5 on incomming calls that instead of ringing go to voicemail after the caller hears 2 rings instead of the usual 4 or more. This issue seems to be unrelated to iOS, as I've experienced this through 5, 6, and now 7. My girlfriend has an iPhone 5 and experiences it as did a client at my office the other week on an iPhone 4S.
After working with both Apple and ATT techsupport, I've come to the idea that when ATT towers can't find an iPhone in the way it is expecting, it assumes the phone is off or unreachable and routes the call to voicemail.
If the phone is within eye shot, I can see a call is coming in because the screen lights up and I see the Caller ID. If I can grab the phone before 2 rings ends, I can answer the call because it is there. It's just not alerting me with a ringtone.
I've learned that voicemail is on a different system so when I get a no ring call, and if the caller leaves a voicemail, I WILL hear the VM alert, which is often how I know I just got a no ring call.
The other ways are: I'll see I have a VM and since my phone is almost always near by, I know I didn't hear the call, and I can also check the Recents and have learned that the call doesn't show up as a missed call either.
So if the caller doesn't leave a VM, I have no way of knowing I missed the call.
Since the worst situation is where I spend most of my time is my office, so that's where I notice the no rings the most, ATT gave me a Cisco 3G Micro Cell which is a tower in your home or office that plugs into your Router and seems to be part VOIP until ATT's system can find a tower with a strong signal on out going calls, how it works on incoming, I'm not sure, but with the the MC I always have 5 bars. Without it, I have 2-3 in the office.
It "seems" that the MC has stopped or dramatically reduced no rings in my office. They will still happen outside the office as there is a problem wither with ATT, or the iPhone, or the relationship between ATT and iPhone not being able to handshake, or whatever you call it in telephony language.
But the MC introduces a new problem. Also internittent. After talking for 10-15 mins, the person I'm talking with complains I'm starting to break up as if I moved to a bad location with interferrence, but I'm usually sitting in my chair and haven't moved at all. I've even gotten up and walked over to the MC which is positioned a foot from my window and held my iPhone right up to it and they still can't hear me as my signal quality to the continues to deteriorate until we are forced to hang up and call back.
Interestingly, I can always hear them fine while my signal deteriorates.
If Verizon did voice and data, I would have switched long time ago. But the odd part is that neither Apple nor ATT are fessing up to knowing about the problem or telling me what it is and what's causing it and if there is a fix in the works.
So.. I present this to the Apple Community and wonder if any of you have any input or similar experiences.
PS: At one point I filed complaint with the FCC which got me a call from the ATT President's office plus a $400 credit and free MC. BTW, if you have signal issues, when you first tell ATT they will try to sell you one for $200. If you stand your ground stating that it is there responsibility to provide service, they will cave very quickly and send you the MC no charge. Not even shipping. They know something's very wrong here.
I sure hope someone has definitive input.