BRUSSELS—Facebook on Thursday secured EU antitrust approval for its acquisition of U.S. customer service startup Kustomer after agreeing to provide rivals free access to its messaging channels for 10 years. The European Commission said the pledge addressed competition concerns. Reuters reported last month that the world’s largest social network would gained conditional EU clearance for the deal. “Our decision today will ensure that innovative rivals and new entrants in the customer relationship management software market can effectively compete,” EU antitrust chief Margrethe Vestager said in a statement. Kustomer, which sells CRM software to businesses so they can communicate with consumers by phone, email, text messages, WhatsApp, Instagram, and other channels, would help Facebook scale up its instant messaging app WhatsApp, which has seen usage soar during the COVID-19 pandemic. A buying spree of startups by big companies has triggered concerns on both sides of the Atlantic, with regulators worried about …