The 2N® Helios IP Eye is a freely available application that not only adds video to any phone, but also provides video surveillance at your entrance.
All you need is a door intercom with a camera and you can watch video without the need for a videophone. When someone rings the bell, a video window pops up automatically and you can immediately see who is standing at the door.
With the Pro licence, you can also unlock the door or turn on the light, directly from the application window. Of course, you can also have video display without audio, and from several intercom units at the once.