Sprint Mystery

I can't figure this out. Maybe y'all can help. So I kept my American cell phone and brought it out here, primarily b/c I have a lot of phone numbers of family and friends, but b/c it's Sprint and Sprint phones don't have SIM cards that you can take out, it doesn't work in China. So basically it has two purposes. 1. phone numbers, and 2. it still has the time and date of back home, so i know what time and date it is back in LA, since i can't always subtract 16 hours and figure out the time. (Despite my ethnicity, math was never my strong point in school.)

So I have my phone on Airplane Mode, meaning that the phone service part is off, meaning that the phone won't automatically start searching for a signal, which is perfect b/c there is no signal it can connect to. Or so I thought. Last week the battery finally died, so I recharged the phone. When I turned the phone back on, it displayed the current time and date of Shanghai. Whoa, wait up yo, what the fck?

I can't understand why my US-based Sprint cell phone that is not accepting any phone signals or service is displaying the current time and date of my current location. What's going on?

http://shangbert.blogspot.com

ps. Yes, it is the same phone as Agent Moss in this season's 24.