Why doesn't my iPhone ring sometimes?

Maybe no one is calling you.

I have had this happen a few times as well and suddenly got the voicemail indicator when I was sitting here with my phone the whole time not even using it. This happened with my AT&T iPhone several times. I also have a Verizon 4S now and it hasn't happened since I got it.

This happened to me yesterday and I got a voicemail alert after the call came in. Mr gdgmacguy, not helpful...

How do you get an answer around here. I don't want to go to the store. It's so crowded.

There isn't really anything you can do to prevent this other than making sure that the phone has a constant good signal. Full bars also mean nothing as you can have one bar and still make a clear call.

This depends on which tower you're connected to. Specifically, a mobile cell has a fixed capacity for the number of concurrent calls it can handle at a given time. The theoretical upper-bound for GSM is about 8,000 simultaneous connections (voice and data), but, in practice it can be much less, depending on the hardware and local topography (not all channels may be available, for instance).

When you get a call going directly to voicemail, it is generally the result of congestion somewhere on the path between you and the caller. If the network's too busy to establish the call, the caller is routed to voicemail and you get a notification of the voicemail sometime later.

The number of bars on the phone reflects the intensity of the radio signal between the phone and the cell tower. It will not give you any indication about how much of the the tower's call or data capacity is being used. It's not at all uncommon that in emergency situations, large numbers of callers saturate their cells and experience an inability to make or receive calls. Sometimes the capacity is reached in non-emergency situations too.

It just started to work again and I am in a different place. Weird. Perhaps it fixed itself. :-)

I noticed this when it is in my pocket. I just thought it was because Apple put the speaker on the bottom of the phone, so now I put the iPhone in my pocket upside down.

Yes. It's not a phone problem. It's not even a provider problem per se, in so far as that your provider may be AT&T, but the operator of the cell tower your phone has associated with may very well be someone else entirely. The poster that saw the problem go away after moving to Verizon probably frequented an area served by an over-capacity GSM tower. By switching to Verizon, he switched cellular technology meaning that his phone was connecting to different towers (TDMA ones), and the ones servicing the areas he frequents weren't over-capacity.

These problems tend to go away with time as the network gets updated. AT&T provides an app called "Mark the Spot" where you can report these problems (and "dead zones") and they use the reports to prioritize their upgrades and deployments (and to request same from third parties).

I've been reading these problems, mine is similar. At random my iPhone 4s does not ring. My husband or daughter will call me on my home phone and ask why I won't answer my cell. I'm sitting right next to it. It never rang. But yet there is a message from them. This happens at least every other day even when I'm out and about. I've been to Apple a few times. They run a test on my phone and tell me nothing is wrong. They say the problem is with Verizon. My husband has the same phone and service. Has never happened to him. I've done resets many times. Issue still continues. I'm frustrated. Any ideas what to do. Apple verified all setting were right. They are.