Can I use the headphone in the Aria 90B set separately with other devices like my smart phone?

You can use the headphone alone with other Bluetooth enabled sound source devices. When use the set, the headphone and USB dongle always auto pair to each other once powered on. To use the headphone with other devices, you need to set it into pairing mode manually, please refer to the following steps to see how: 

Step 1: Unplug the USB dongle, so that the headphones will be available for other devices.
Step 2: Power on the headphone, slide the power switch to the middle position as shown in the following:
                                 
Step3: Enter Pairing Mode, slide the power switch to the Bluetooth icon side and HOLD it there for 2 seconds until the LED indicator alternates between flashing RED & BLUE, you will also hear the voice prompt saying "Pairing".
                    

Step 4: Pair them up, in the Bluetooth settings menu on your device, locate "Avantree Aria 90", click "Pair" to connect the headphone. Once connected, you'll hear "connected" in the headphone.

Notes of Reconnecting:
1. The Bluetooth name of the headphone is “Avantree AS90” when use the headphone alone.

2. It does not do auto reconnection when use the headphone with other Bluetooth devices instead of the USB dongle. So you need to click “pair” on your device or slide the headphone power switch to the Bluetooth icon to reconnect them.

3. When the headphone is paired with another device instead of the dongle, the dongle can not reconnect to it even when plugged in. On the contrary, it will reconnect as long as the headphone is disconnected from other devices and powered on.