Unable to communicate with ATC; Mooney M20 pilot descended without clearance to escape icing conditions.

Narrative

After departing PFN; midway through the flight; noticed clouds below began to thicken. Called weather service from airplane. Asked about destination airport conditions (ZZZ). They told me at ZZZ the clouds were broken and improving. I read that it would be scattered clouds by the time I arrived. As I got close; the clouds began to rise all around the airplane. It was an updraft that I was in. I called the Controller. Told him I would need instrument clearance to descend. He gave me a heading of 270 degrees; clear to 6;000 FT. At 6;000 FT; ice rapidly began to accumulate. Calling the Controller; there was no answer. At one point; I did get a brief relay from another airplane. Controller couldn't hear me; so I pressed ID button on the transponder. He saw it and began communicating with it. I couldn't let Controller know I was icing up. I started emergency descent to 4;000 FT. We broke out of clouds and began to defrost. Communication per radio returned back to VFR. It is my belief; if the weather information had been more specific; this would have been avoided. Also; if the ATC Controller had been informed of the icing conditions; he could have cleared me to 4;000 FT sooner. When the radio went out; the Controller should have been the first one to suggest using the ID button.