What is the wattage of my iPhone? I am trying to make a transportable charger for iPhones, but before I can start this I need to know how much power my iPhone uses when I make an emergency call.  

If nobody knows this, I will be glad to have any information related to this.
Anandtech has some nice charts detailing the wattage of the iPhone 4S running various apps, which could be a good starting point for you. 

You may also want to check out existing kits/projects, such as MintyBoost - they seem to work reasonably well with iPhones. There's a specific MintyBoost page detailing Apple device charging that may also yield some useful info.