NEW YORK — AT&T Inc. said Friday that the shutdown of its second-generation, or ‘‘2G,’’ wireless network will be complete by the end of 2016, a process that will force customers with older phones to upgrade to ‘‘3G’’ or ‘‘4G’’ handsets.

In a regulatory filing, the Dallas company said 12 percent of its customers on contract-based plans, or 8.4 million people, have 2G phones.