I have an old knight and hail call that I use all the time that rarely freezes, even in bone chilling -30 that we are having today.
I keep it on the dash between calls to let the heater get rid of any water that's still in the call. I find that even half way through the stand if it does get frozen a good burst will clear it out. I also tend to turn it around and breath into before a series just to thaw it out. Sounds harder then it is really.
Scotch makes a shacker type call that works extreemly well in the cold. And by squeezing the "tube" yoiu can get some sounds that are almost impossible to make with a mouth call.
