I have had my iPhone 3GS for a little over two years now and been with AT&T for 3 1/2 years appr.
For about the last year I have been having periodic issues with phone calls going straight to voicemail and it seems to be getting worse. At this point, it seems at least half my calls go straight to voicemail without the phone ringing. I didn't have this issue when I first got the phone, but started noticing this problem periodically (and dropped calls) after upgrading my 3GS to IOS 4 software. Never had this particular problem with my Blackberry Curve prior to that (non-3GS).
This problem can happen in any conditions. It doesn't seem to have a correlation with my signal strength and usage. I can have 5 bars 3GS signal and be not using data and it still have this happen.
I moved to Virginia from West Virginia in April, but was having issues before that. But they have gotten a little worse since moving here (25 miles out of DC). I currently still have my WV phone number. I was waiting to get new number when I get new phone (Kinda waiting on iPhone 5
). I am NOT using the microcell.
At this point, I'm trying to figure out if it is the phone, the software, or the service. Any help is appreciated. 
Have you considered that it could be an AT&T network problem in your area, especially since it's happening on both of your phones? Or maybe even a sim card problem? Have you done any troubleshooting?
You may think the 4s is "a really bad phone" but I do not. I think it's a great phone and I haven't had one iota of a problem with mine.
citizen_jane wrote:I have the same problem with my 4s but my husband also has the problem on his 3gs. Unfornately, it's just one of many problems I have making and receiving calls with my 4s... dropped calls, calls where the other person says "you're cutting in and out", calls where I can't hear the other person but they can hear me. The 4s is a great little computer but a really bad phone.
I was actually responding to citizenjane.
But if you haven't already done so then I suggest a trip to your nearest AT&T store to replace your sim card. If you have already done that then maybe you need to make an appointment with the Apple Genius bar so they can make sure it's not a hardware problem with the iPhone.
http://www.apple.com/retail/geniusbar/
rlrich wrote:it's not a ATT network problem and it's not specific to one version (3G or 4S).
we have four iphones in this house and three work with no problems -- just one has random calls go straight to voice mail .
1. as a test I have had persons who are trying to call me but getting voice mail instead call another of the iphones that are sitting with me in the same room. those calls go through no problem on the second phone.
2. it used to be that my 3G phone was having the trouble so I upgraded to 4S and it still has the same problem. so it's not the actual phone itself
