We operated several types of phone, analogue, CDMA, and digital. All were hard wired into the system, with audio coming through on button 4, and pull the transmit trigger to talk.
Analogue worked OK, but didn't have the fancy features and was phased out in OZ some years ago. CDMA was the replacement, but its performance is patchy, and often it would show 3 signal strength bars, but when you hit send it would drop off.
Digital is OK around major centres, but not enough coverage where choppers go. Probably not a problem in Hong Kong, though...
Never had a comment from any service provider, they just sent their bills and we paid them.
Now running a satellite phone. Despite the sales blurb from the supplier that it was a complete kit, it wasn't, and the stuff they did provide shorted out some components. It only works now because our engineer discarded some bits and created some new bits.
The only real danger with a phone in the cockpit is answering it when it rings at the wrong time. Heard tell of a pilot in a retractable who answered a call while joining the circuit, and didn't put the wheels down, did a gutser. Somehow didn't react to the warning noises and lights. Must have been a call from 1800-suck-my-t1ts or something!