Hi
It is bad and affects a lot of people, I've had my phone changed 3 times all with the same issue, about 20 other people I know who have iPhone 4s have this problem.
You will get a lot of fanboys here defending apple saying nothing is wrong with the phone and don't hold it that way, but the truth is, this problem exists in a lot of iPhone 4s if not all of them.
Uh... The problem exists with any RF transceiver equipped device. If you test a Wi-Fi router in a room with aluminum walls and can't get a signal when leaving the room... Oh yes.. Must be the router.
😀
As far as your comment to it being an issue with so many people; try choosing a cellular service company that best fits your frequented regions, instead of basing your decision strictly around a phone.
I have been with AT&T, and briefly Cingular before the switch, for quite some time now. I live in a pretty rural area where Verizon controls the majority of coverage because they purchased a dieing company called Cellular 2000, which invested highly in covering the state of MN as best they could.
My point is this, I've had Nokias, Samsungs, Motorolas (those with external and those with the now common internal antennas), but every cell phone I had struggled for connectivity in the same areas. Of course, coverage has changed a bit for both over the years but it actually still remains generally the same, with some improvements here and there.
Put simply, it is a problem but it's RF technology limitations, not an iPhone flaw.
P.S. I'm happy with AT&T for my uses, which is why I've been comfortable with buying and upgrading to new iPhones. That isn't true for everyone, so make your choices appropriately.