Having lived in South America for a decade, I constantly heard/saw the term "un llamado" used for "a phone call" (phone/internet businesses even called themselves 'Centros de Llamados'). Of course, the only term I had known previously (in Spain/Mexico) had been "una llamada". Since then, I have seen the two used somewhat interchangeably. Could someone please explain the difference in the two terms? Is it a difference in grammatical correctness or just a regional preference? Thanks in advance!