I think there is a potentially emerging market here for portable refrigeration units; I'm going to call mine the Personal iPhone Refrigeration Pal or PiRP for short. Just clip it on the side of your phone - weight is a negligible 10 lbs; they say weight bearing exercises are important, so it is a bonus feature at no additional charge.
In all seriousness, I haven't noticed any increases in thermal output from any of my devices with iOS 7; just an annoying inability for some of them to connect to WPA2 protected networks. I couldn't imagine having to put my phone in a freezer just to get the wifi to work.
What is so frustrating about all of this is, as mentioned above, it seems an OS update is causing hardware issues. It's so annoying that my phone was running great on iOS 6 but a simple upgrade to 7 has crippled it in terms of wifi flexibility. My iPad also resets itself about once or twice a week, particularly when using the iTunes or App Store apps, which rarely ever happened under iOS 6.
Ah well, good luck with calling Apple.