Am I allowed to take photos on an airplane with my DSLR?

Let's say I have a Nikon D5000 DSLR camera aboard a United Airlines flight. Would I be able to take pictures with my camera? If not, may I use a video camera such as a Canon Vixia? If not may I use my iPhone? What is and is not allowed? And It is Chicago O'Hare airport to San Diego if that matters… Thank you.

Photography and videos are at the discretion of the airline. Check United's website for information. Electronic devices, including digital cameras, video cameras and phones must be off during landing and takeoff.

You might, But not during landing or take-off!
I've done it before with American Airlines, So I'd say you can.