Well, let's see ... first if you're getting anything from being in contact with the antenna, it's through conduction not radiation.
And if what you're feeling is not just a product of holding your fingers in an odd position for 20 minutes, then its just a low level electrical current. This seems probable, as the chances are your fingers will moisten slightly from being in one place for so long, lowering resistance and increasing current flow to the point where you can just feel it.
I can't personally, but then I don't think I've actually held a cell-phone to make a call in the last 4 years.
And yes, electromagentic energy reduces with the square of the distance from the source, which over the 1/4" of an inch the antenna in another phone was from the face, means bugger all.
You can't "feel" radiation directly, only the secondary effects. Usually heating, which can be direct heating (infrared, as with sunlight) or with microwave radiation (which is what GSM is based on), you'd feel it as heating resulting from the vibration of, principally, water in your cells and the friction this produces. It wouldn't feel like tingling.