Japan’s NEC Corp. is buying CSG Systems International Inc., a US supplier of customer care and billing services for telecom companies, for around $2.9 billion in a move to shore up operations abroad.CSG stockholders will receive $80.70 per share in cash, the Tokyo-based industrial electronics group said Wednesday. That represents a roughly 17% premium to CSG’s last closing price of $68.75. The deal would make the US company a wholly-owned subsidiary of NEC, whose businesses span personal compute...