Unclebuck
I have only had my custom calls freeze a few times. The air chamber designed was taken into consideration when making the call, most of the saliva falls short of the reed and there is no metal wall around the reed to collect saliva. But condensation still forms some ice over time on the right nights. How ever if it did freeze up I just slowly blow worm air down the call and it will unfreeze because there are no real ice balls just condensation. However to keep closed reeds calls working wash them in warm water before each hunt. Saliva will build up and dries after each outing. This in turn will start to restrict air flow and the call is only working at half it,s reed spacing off the reed bridge and that space is very close to begin with. To wash an open reed call just turn on your sink with worm water. Run the water in from the exhaust side of the call. This will let water flow between the reed and the reed bridge. Then blow on the call from the exhaust side of the call to remove some of the water left. Then blow your call like normal, This will help break lose and remove old saliva.
Some times this whole method needs done two or three times to remove dried saliva. Now as far as other peoples close reed calls they will freeze up pretty easy because of there design, but cleaning them will still help. You know what, I better go clean mine now, I did not do it since last years season yet. Ya know how it is when you get home from hunting the last thing I think about is wanting to clean my calls.