National Grid Transco is to buy the UK business of Crown Castle International for £1.1bn ($2bn).
Crown Castle UK operates mobile and TV masts
Under the deal, the UK energy group will acquire Crown Castle's network of mobile masts and broadcasting towers.
Crown Castle UK will be merged with National Grid's own telecoms infrastructure business, Gridcom, bringing annual savings of £18m.
Crown Castle UK's broadcasting towers are used in the transmission of analogue and digital TV and radio.
"High quality, low risk"
The transmitter company is part of a consortium behind the Freeview digital TV service, which also includes broadcasters the BBC and BSkyB.
National Grid said the combined company would be "well positioned for the move towards digital television" in the UK.
The takeover adds 3,500 mobile masts and 750 television towers to National Grid's own portfolio of 1,400 sites.
Roger Urwin, National Grid chief executive, said: "Crown Castle UK is a high quality infrastructure business with low risk characteristics."
He said: "Combining Crown Castle UK with Gridcom will, we believe, create value from integration savings and the opportunities presented by growth in the mobile and
broadcast infrastructure markets."