In 2002, after Extremadura dropped another category to the third level, Kalla signed with VfL Bochum in Germany– he scored five times in his last season, second-best in the squad – but the club was relegated from the Bundesliga. He also received a three-match ban for anti-doping rules breaching, in late 2003.
Kalla gained 63 caps for Cameroon, and was a participant at three consecutive FIFA World Cups: 1994, 1998 and 2002. In the first he (aged 19) played all the matches and minutes, often being partnered by another youngster, Rigobert Song (18), in an eventual group stage exit.
After the 2002 World Cup, Kalla announced to retire from the national team due to conflicts with the Federation structure, which he accused of poor organization, but eventually changed his mind.
Initially summoned for the 2006 Africa Cup of Nations, Kalla was forced to withdraw due to injury, and retired for the second and definitive time.