While programming my Icom radio it has MR (memory)channels, VFO (Variable Freq) channels and Call Channels. What are call channels as comparred to memory or vfo channels? What is their use?
From the radio device perspective, a call channel is not that different from a regular memory channel, except it doesn't have a number, there's usually one per band, and typically you can get to it quickly with a single button press. It may be preprogrammed with the conventional per band calling frequencies, but typically it's just a regular memory so you can change it.
From the use perspective, most bands have a calling frequency as part of the band plan. By convention you would call on that frequency to initiate a contact and then move off to another frequency to rag chew so you don't clog it up. More typically, on a band that isn't very busy, the activity is so low it wouldn't matter if you moved off or not.
Near highways, sometimes the calling frequency is used for unplanned local vehicle to vehicle contacts in a small area. For this use, a continuing conversation on the calling freqency is ok, but you should be sure to leave large gaps between every transmission so that others can join in or use the frequency for calling others.
The calling frequency is also part of the wilderness protocol, which can be used for emergency call outs. So if you are using the calling frequency, by this protocol you are suppose to listen for the first 5 minutes of each hour in case someone is calling for help and not resume normal use sooner than 4 minutes after the hour.
In the US, the FM calling frequency for 2m is 146.520