One of the fun air-gesture features of the Samsung Galaxy S4 is called air call-accept, which lets you answer incoming calls by waving your hand over the phone. To give similar functionality to users of other Android phones, an XDA Developers member published a new app called Air Call-Accept.
Air Call-Accept is enabled by default after installation. Opening the app reveals the simple on/off slider. On some phones, you'll also need to make sure that the proximity sensor is enabled. On the Galaxy S3, go to Settings > Motion. With the free version of Air Call-Accept, you can wave your hand over the proximity sensor to answer incoming calls. The paid version also allows you to reject calls, turn on the speaker when answering, and send an SMS when rejecting calls.
Keep in mind that the app has some bugs that the developer still needs to iron out. Forum members over at XDA Developers have noticed that Air Call-Accept automatically answers calls when the phone is in a pocket or when a flip cover is installed on the phone.