Was having an issue with my 3gs after the IOS 6 upgrade. Wouldnt see or connect to any wireless network. Raised support calls with Apple but got the feeling that with my phone being 600+ days beyond warranty, (Was reminded of this SEVERAL times during the call), that they wasnt really interested despite that it was working fine on 5.1.
Anyway, after reading several pages of people experiencing the same issues, I bit the bullet and invested a small fortune in replacing the Wireless antenna, (£2.15 from ebay), and this has solved the problem.
The conspiracy side of my brain is now asking is this a tactical ploy by apple to force us that like our older phones the purcahse newer ones???