WASHINGTON -- AT&T Inc. alleged Friday that Google Inc.'s Google Voice service is improperly preventing consumers from calling certain phone numbers, in violation of federal call-blocking rules.

In a letter to the Federal Communications Commission, the phone giant accused Google of violating rules designed to ensure phone companies connect all calls. AT&T also accused Google of violating "net neutrality" principles, which are designed to ensure consumers can use any legal Internet services they want.

Google...