So......Wifi is always on? Well that contributes to the heat, any services running, how fast and actively you go through an app, things of that nature, etc. For example, my 920 will be cool, no heat problems at all, then I'll open up Lomorgram (no WiFi on at all) and starting applying filters, then another filter, then another, and 10-15 filters later, my phone is warm. It's because I was blazing through the application features.