An accurate time signal



I'm looking for an accurate time signal. Don't have a shortwave to
pickup WWV.

I don't need a signal accurate to a microsecond; about +/- 1/2 second
of the correct time is what I seek. Here are some sources I've
considered:

-WCCO-AM CBS 830 radio (Minneapolis) 'ping' at the top of the hour.

-My cell phone time.

http://www.johnweeks.com/stuff/navyclock.html
http://www.time.gov/timezone.cgi?Central/d/-6

These signals sometimes differ by 10 seconds. Who should I believe?

With the internet sources, I'm concerned too about the download time:
I'm on dial-up.

I have a gps also, although it's currently out on loan.

.