C172 pilot encountered icing and lost communications on IFR cross-country flight.

Narrative

Received in-person standard weather briefing at the FSS prior to departure. VFR not recommended due to low ceilings mid-route. Reports and forecasts indicated low clouds and no significant icing potential. Pilot reports indicated low tops (1000 - 1500 FT) and no icing. An IFR flight plan was filed at 8000 MSL cruise. Approx 150 NM from destination encountered multiple layers to 10;000 MSL and decreasing OAT with moderate precipitation. Encountered light icing at 8;000; requested and received clearance to 6;000 MSL where ice accumulation melted and no new accumulation. Temperature continued to drop and approximately 20 minutes later began accumulating ice at 6;000 MSL. Requested descent to alternate airport or course reversal from Center but; probably due to distance; was unable to communicate with ATC despite multiple attempts on both current and last assigned frequencies. Tried on both aircraft transmitters. Also attempted relay from any other aircraft on either frequency but received no response. After attempting communication with ATC for perhaps 5-10 minutes; with no response and ice accumulating at light - moderate rate; we encountered VFR conditions. Made several 'blind' transmissions that we were going to descend in VFR; but received no reply on any frequency. We descended to below the cloud bases and continued to destination in VFR conditions with no further icing. Approx 30 NM west-northwest of destination regained contact with Center and informed them of our position; altitude; VFR conditions and intentions and canceled our IFR flight plan. Continued VFR and landed. In a future similar situation I would pay more attention to forecast temperatures aloft even if there is no forecast icing. I would also attempt communications on 121.5; and via transponder emergency codes; which I did not do since I did not consider our situation an emergency because there were the options of a diversion or a VFR descent.