A person who specializes in or practices dialling, particularly someone skilled at making telephone calls.
From 'dial' plus the agent suffix '-ist' (one who practices or specializes in something), following the pattern of 'artist' or 'pianist'.
The term 'diallist' was sometimes used humorously in the early telephone era to refer to someone obsessed with the latest communication technology—the 'tech enthusiast' of their time!
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