HTC Mini, a small, basic phone that comes with the Butterfly in China is meant to be used as a companion with its larger sibling.
The Mini is NFC- and Bluetooth-enabled, and it works with the large phone in your pocket, displaying notifications, texts etc.
It can also help you locate your lost smartphone by triggering an alert in the lost phone. It can also act as a remote if you use your smartphone to watch something on a TV. It also acts as a remote trigger for the Butterfly's camera.