At&T Inc. has agreed to purchase T-Mobile USA from Deutsche Telekom for an estimated $39 billion in cash and stock, pending regulatory approval.

The deal would create America’s largest mobile-phone company.

According to a statement released by the companies, the purchase price will include $25 billion in cash and the balance in AT&T stock.

The key question is what the move will mean for the millions of both At&T and T-Mobile customers.

Analysts predict the merger would be a positive for AT&T customers, especially those in the Bay Area, who have continually struggled with dropped calls and poor network service. The company is also pledging to invest more in broadband coverage.

For T-Mobile customers, users with T-Mobile phones with “3G” wireless broadband won’t get that service any more. At&T is expected to offer new phones with access to AT&T’s 3G network.

The Federal Communications Commission and federal antitrust authorities are expected to review the makeup of the deal and could come to a decision in the next 12 months.