The time of day is broadcast on radio stations WWV and WWVH, which transmit in the shortwave bands, on 2.5, 5, 10, 15, 20 MHz. The time is announced every minute, and at other times there is a steady beeping. Any shortwave receiver should be able to pick up these broadcasts - the particular frequency you can receive will vary with location and time of day.
You can also hear the NIST's WWV broadcasts via the telephone. The number is (303) 499-7111.