Nikos, do you have your phone in a case? If so, have you removed it to see if it makes a difference?
No case here. I'm hesitant to get a replacement because I'm happy with the phone outside of this issue. I'll wait a bit since we have 30 days for a 'no questions asked' replacement.
I guess the real test will be at work tomorrow. We have company-wide WiFi. My 4S would get full signal but I'm not sure where the access points are. If this still connects, I'd be hard pressed to say it's a hardware issue. Then again, if only some are experiencing the issue, it wouldn't make as much sense for it to be software.