Many people assume that they need to invest in an expensive virtual reality headset to experience 3D video and VR games. In reality, you could use a cardboard headset with your smartphone to get started. The NOON VR headset is a bit more polished than cheap cardboard headsets but lets you use your iOS or Android device for virtual reality.
NOON VR is compatible with smartphones 4.7″ or larger. The companion app is available for free. The package contains an adjustable headband, detachable frame, protective cover, and everything you need to get started. Not the cheapest VR headset though.