I can vouch for this heating method. I purchased a 4S with greyed out wifi, and n/a for the wifi address under the settings. The bluetooth was showing an address under settings but would continuously be initialising itself.
I removed the back, battery and EMP shield as per the instructions above, and warmed the wifi chip with the tip of my soldering iron for a couple of minutes (I don't have a hair dryer).
I re-assembled the phone, turned it on and BAM....the bluetooth was on straight away. I went into wifi, which was now no longer greyed out, selected my router and connected.
I can turn the wifi and bluetooth on and off and they connect successfully every time.
100% perfect result!