I realised some of the big cost was HSBC. I needed to get in contact with them regarding MPF. I rang using Skype but they refused (totally and utterly refused) to allow me to wait in a (relatively cheap) skype queue. NOPE. THEY INSISTED on ringing me back. I tried all day to get through using other means (email, chat on the app, my relationship manager) - nope. They had to ring me. I found out this is several hundred dollars of the cost. They rang me 4 times in the end although I doubt we spoke for more than 10 minutes total.
Just check if you don't pay roaming fee for them just to contact your voice mail. If I recall correctly that was the case many years ago. So even if you don't pick up and it goes to voice mail they will charge you as voice mail is considered the same as picking up the phone. Maybe things have changed though (although it's HK so doubt that)