Crown Castle ( CCI) agreed to acquire Global Signal ( GSL) for $4 billion in cash and stock, creating a wireless tower giant. Houston-based Crown Castle said the combined company will have over 24,000 wireless sites and 16,240 towers in the top 100 basic trading areas -- the most of any tower company. "We expect this extraordinary combination of companies with the most towers in the best markets to create significant value for our customers and shareholders," said Crown Castle chief John P. Kelly. "The complementary nature of our U.S. portfolios will result in a high-quality, diversified customer base, with 76% of site rental revenues from the four largest U.S. wireless carriers." The merger is expected to generate cost synergies of between $12 million and $15 million annually, which are expected to be realized within 12 months after closing. Global Signal holders will get 1.61 Crown Castle shares or $55.95 in cash for each Global Signal share they hold. Crown Castle will pay as much as $550 million in cash in the deal and the rest in stock. The agreement gives Global Signal holders a 12% premium to Thursday's closing prices. Three Global Signal directors will join the Crown Castle board, boosting board membership to 13. Kelly and Crown Castle financial chief Ben Moreland will stay in their jobs in the combined company.