Try refreshing the settings on your iphone and then you could try pressing 'forget this network', and re enter your router details.
There is quite a bit of info on further resolutions on the internet too you could try before possibly arriving to the final resolution of visiting your genius barr.
Hope all goes well for you.
I tend to think its ios6 not the iphone thats at fault here as many owners reported this issue after updating to ios6 !