Use of the term "Heavy" is required in the terminal environment by regulations. From the 7110.65:
2-4-14. WORDS AND PHRASES
Use the words or phrases in radiotelephone and interphone communication as contained in the P/CG. The word "heavy" shall be used as part of the identification of heavy jet aircraft as follow:
TERMINAL. In all communications with or about heavy jet aircraft.
EN ROUTE. The use of the word heavy may be omitted except as follows:
a. In communications with a terminal facility about heavy jet operations.
b. In communications with or about heavy jet aircraft with regard to an airport where the en route center is providing approach control service.
c. In communications with or about heavy jet aircraft when the separation from a following aircraft may become less than 5 miles by approved procedure.
d. When issuing traffic advisories.
EXAMPLE-
"United Fifty-Eight Heavy."
NOTE-
Most airlines will use the word "heavy" following the company prefix and flight number when establishing communications or when changing frequencies within a terminal facility's area.