Summary Box: Cellphone cos. to warn as limits near

THE WARNINGS: Cellphone companies will let subscribers know before they go over their monthly limits for calling minutes, text messages and data use. The warnings will arrive as text messages, and subscribers won’t need to sign up for them ? they’ll arrive automatically.

WHEN THIS WILL HAPPEN: Officials say companies will have warnings in place on at least half their plans in a year and all of them in two years.

WHAT PROMPTED THIS: The alerts are voluntary for the phone companies, but the development comes in response to a threat of federal regulation.