BNI,
The pairing is straight forward as per the Lightspeed manual.
Once the headset is paired, to answer an incoming call, you briefly press the Bluetooth button on the battery box.
To make a call, press the Bluetooth button once and talk to Siri.
Anyway, have you tested "Hey Siri, call ATC" in the air yet? The reason I ask is the "Hey Siri" callout function only works if the iPhone is plugged into mains/external battery. Just a forewarning, in case you didn't know!
I didn't want to call ATC on their emergency number, so my son acted as substitute.
It worked perfectly, so I was surprised by your comment. After some research, I discovered that the Siri "always on" feature was introduced with the iPhone 6s, which I have. On an older phone that supports Siri, if the phone is not charging, you need to press the Home button while talking to Siri.
A comment on the Zulu 3 headset. A year ago, my headset was stolen and I had to replace it, so I considered the Zulu 3. However, it is much more expensive and it requires more batteries, so the battery box is much bigger. I stuck with the Zulu 2.