HumMii allows you to send funny sounds to your friends as push notification.
Add your friends to the friend list, select one you want to hum to and send a funny sound directly on his or her device.
Please make sure to allow HumMii receiving push notifications. Otherwise you cannot hear when your friends are trying to hum you!
If any user starts to bug you just use the block list to stop him/her sending sounds to you. But dont block anybody too long, because humming makes a lot of fun!