As a long time reader, I'm pretty severely disappointed by the responses to this post. No discussion of NTP, or GSM time distribution, or CDMA time distribution, or shortwave radio, or ANYFUCKINGTHING relevant to the poster's question.
Where did the knowledgeable people go? Because I really don't need some douchenozzle to tell me that the Amazon fire has a clock app, and see that that post has been rated +4?!?!?! WTF?!??!?!
Give mod points motherfuckers and I will clean up this mess.