MTN Group Ltd. and Airtel Africa Plc were given the green light to resume the sale of new SIM cards in Nigeria following the implementation of a new policy linking them to national ID numbers. Wireless operators were ordered to stop activities in December for an unspecified time, raising concerns about growth potential in Africa’s most populous country. MTN’s local unit is the West African country’s biggest wireless operator, while Airtel Africa, which listed in Lagos and London in 2019, is just ahead of local operator Globacom Ltd. as the country’s second-largest. Nigeria is also MTN’s largest and most profitable market. Nigeria has battled a deadly Islamist insurgency in the northeast of the country for two decades, and sees the tighter monitoring of mobile-phone use as a potential way to combat the problem. The regulator fined MTN more than $5 billion in 2015 for missing a deadline to disconnect unregistered subscribers, triggering a share-price crash and a year of negotiations before a settlement was reached.