Plural form of dialler; multiple people or devices that dial telephone numbers.
Simply the plural of 'dialler' using the standard English '-s' suffix to indicate more than one.
In busy call centers of the 1960s-80s, teams of human diallers would sit at switchboards handling hundreds of calls daily—it was tedious, repetitive work that was later automated by mechanical diallers.
Complete word intelligence in one call. Free tier — 50 lookups/day.