Callejas compiled a record of 36 wins and 4 defeats as an amateur boxer, and in 1979, he decided to turn professional. That he did on the night of February 18 of that year.He was beaten by Jose Parrilla by a decision in four rounds. For his next three bouts, he travelled around some of the other Caribbean islands, gaining revenge over Parrilla in St. Croix for his first professional win, knocking out Wilt Jones in one round in St. Marteen for his first knockout and beating Albert Pagan, also by a knockout, in five.