Here's a common situation: You're holding your cell phone and, all of a sudden, you see a notification that you have a voice mail. You think that's strange since you had the cell phone right there in your hand and didn't see any call coming in. You listen to the voice mail and then you call the person back who left the message. That person tells you that they tried to reach you but the call went directly into voice mail. Again, you think how very strange it is. How could the call go directly into voice mail if you were holding the cell phone and the service signal looks strong?
I'll bet everyone with a cell phone has had this happen to them a number of times and I'll bet that you think that it shouldn't have happened. Well, there's a rational explanation for what's causing this problem. And I have a suggestion as to how the wireless operators can fix it.
According to AT&T Analyst Relations, there are three primary scenarios in which cell phone calls get routed to voice mail: in an out-of-coverage area, if there is a network outage or if the cell phone's "Call Forwarding Immediate" feature is turned on.
I strongly suspect that the primary culprit underlying the problem may be network congestion such as when there are too many calls initiated within the range of nearby cell phone towers. In the congested area, the network would treat some of the calls as if they were out of coverage and automatically forward them to voice mail.
Here's what I believe happens when you make a call in a congested area. You hit "Enter" or "Send" on your cell phone, which initiates the call. But if the network is congested in your area (that is, too many calls being managed by the nearest cell towers), then I believe that the network treats the additional incoming calls as if they were out of the coverage area and sends the calls automatically to the recipient's voice mail. He or she then receives a "voice mail waiting" notification later on their phone-without it ever ringing.
The frequency of the network not completing the call is definitely increasing due to more wireless subscribers and usage-especially in densely populated areas such as major cities. And I've noticed that there's increased frequency of calls going automatically to voice mail when you're at the intersection of two busy freeways (such as the I-75 and I-285 intersection in Atlanta or the Bayshore Freeway and Highway 17 intersection in San Jose). There are many other freeway intersections with dense cross traffic, especially during rush hour.