In the late 1980s, Kullamäe was a member of the U-17 USSR Basketball team (coached by Modestas Paulauskas) and the U-19 USSR Basketball team (coached by Stanislav Eremin). He won a bronze medal with the USSR team at the FIBA Europe Under-16 Championship in 1987. Kullamäe was a member of Estonia national basketball team between 1993 and 1995, 1998 and 2001, and in 2004 and 2007 (when he served as captain). His national team career-high score was 32 points, which was obtained during a match against Lithuania in autumn 1994, as part of the EuroBasket 1995 qualifying round. Kullamäe was also a member of the Estonian EuroBasket 1993 squad.