The sun emits very powerful visible and ultraviolet radiation; although sunglasses are good for blocking some of this light when it's reflected off of other surfaces, they should ABSOLUTELY NOT be used to looking directly at the sun, because they're not nearly strong enough. The same goes for 3D glasses. Using a cell phone camera to image the sun won't hurt yours eyes (since all you're looking at is the image of the sun on the cell phone screen, not the sun directly), but the same powerful radiation can damage the camera itself. If you want to observe the sun, the easiest method is to either view it indirectly using a pinhole projector (poke a hole in a piece of paper or cardboard, and shine the sunlight through the hole onto a screen like a wall), or to view it directly using a pair of eclipse glasses. These are very inexpensive and you can find them at any telescope store; they're very powerful and block almost all the light that reaches them, so you can view the sun through them safely. I hope this helps!

Note from ScienceLine moderator: The following link has the instructions of an easy way to build a pinhole camera. I just built one with my son yesterday!

It depends on the eclipse - the recent annular eclipse, no, you need the full eye protection that astronomers use when looking at the sun when it is not eclipsed. Other eclipses, where the moon is closer to the earth, you can look right at it without any protection at all.