Same problem as everyone else. I have two iphone 4S devices, one for me and the second for my wife. Mine started giving me problems a day ago, quite randomly and out of the blue. Oddly my wife's continues to work fine, which would seem to suggest a hardware issue of some sort. This evening I also did a full upgrade of iOS to 6.1.3 (by wire to get the entire 1GB operating system), but no dice.
When I initially discovered the problem and came to the discussion forum there was some advice to reset the network settings. I did this and the 'greyed out' problem seemed to clear up in the sense that Wifi was enabled; however, it would still not connect because it could not detect any wireless networks in the area. Trying to manually enter my SSID and password also failed with a "cannot scan for networks" error message. I also note that, afterwards, turning my phone off and on again caused the "wifi greyed out" problem to resurface. And now resetting the network settings will not re-enable it. This is precisely why a team of Apply engineers should be working on this problem ...
This entire troubleshooting exercise has been completely frustrating and an incredible waste of time. I hope they resolve it soon. This type of issue, as significant as it is with respect to the number of users affected, impact on usability, and incremental cost in terms of excessive celllular data usage and lost time/productivity (as one is necessarily reliant on slower data through the cell networks) certainly provides a good reason to consider a competitor product the next time one has to think about upgrading their device.
For all the bells and whistles Apple needs to get the basics right. And that goes not only for its product, but equally (or more) importantly, for its product support!
Signed,
One very unhappy user ...
