Developers of Camera+ have tried to add a very useful update to the Camera+ application by adding the ability to take pictures with the volume buttons, but Apple has rejected the update and saying, a function like this might confuse users if they used the volume keys for another job. But you can find after the break how to enable this function.
Simply, just install Camera+ from here then open Safari at Camplus://enablevolumesnap. Now you can take pictures using the volume buttons.
Requirements:Compatible with iPhone, iPod touch, and iPad. Requires iPhone OS 3.1 or later.