A week later, also as a substitute at Murrayfield, he scored his first international try in the 34–22 win against the Pacific Islands, and seven days after that he made his first start in the match against Australia.
His under-19 debut was in the team who beat the Australian Schools at Greenock in December 2001, and he went on to play in all four of Scotland’s matches in the 2002 IRB/FIRA world junior championship in Italy, scoring two tries, one against France and the other in the 17–10 victory against England at Treviso.
Callam played in four of Scotland’s under-21 Six Nations matches in 2003, but he missed that age group’s world cup in England in June of that year because of injury.
He played for the Scottish Districts under-21 team who beat New Zealand Youth at Stirling in November 2003, and he subsequently captained Scotland in all five under-21 internationals in 2004, scoring a try in the games against Italy and France.
He also captained his country during the IRB Under-21 World Championship in Scotland in June 2004 before an injury forced him to withdraw from the competition.