Long overdue cell phone feature
For the past year, the lack of the following function on modern cell phones has really bothered me.

The ability to turn cell phones silent for a given duration. Instead of having a switch that makes the cell phone quiet or noisy, there should be an option where I can tell my cell phone;

"Be silent for the next 3 hours"
or
"Be silent everyday from 10pm to 8am"

I can't believe the programming would be that difficult, and with the majority of phone functionality based in the phoneOS these days, I doubt it's even much of a technical hurdle.
My iPhone, for instance, has an interface within the programming where I can, using the software interface, change the ringer volume, vibrate features, etc. Surely the programming to allow "Silent for this duration" would not be difficult. No more forgetting to turn your ringer on after movies. No more being awaken by errant calls or text messages while asleep...or, if you turn off your ringer at night, no more worries about turning it back on in the morning.

So simple, so useful...how does this not exist?

Addendum
I sent this post, pretty much verbatim, to the Apple as an enhancement request for the iPhone.