People collect information for all types of reasons, especially in Hong Kong. You can find the rules in the HK personal data privacy ordinance. This is about behaviour in a professional scenario. Keep in mind that from individual to individual things can be different.
In a work environment, you will meet people and collect information. The only use allowed for the information is the reason why you collected it. Should you need or want to pass on that information you need to get the person’s approval to do so.
Also when you give you data to someone, they should notify you when they add you on any subscription list. On April 1st 2013, there was amendments about all current subscriptions. They all had to be re-consented to by the subscribers. To comply, websites sent to their mailing list an email. The message said: “this is to notify you and should not take any action you approve to being on our mailing list”. Hence to unsubscribe you needed to do so yourself on the given link on the email. Everyone received a whole bunch on emails at that period.
When it come to telephone numbers the same can happen. The company puts you on their data list and they can contact you for extra offers that they are trying to sell. The magic word for that in English, to remove your details from the list is: opt-out. In Effect the caller should then put you on the do not contact list. The process to be change within the whole company might take a few days. But after that should someone call you again they are committing an offence.
I have yet to have found the Cantonese version of that word.
As for your friends, everyone exchanges contact very often, as it is part of the essence of this city in a way. As a courtesy I always ask the person of which the contact I want to share if it is ok with them if I do so. So that the person does not feel obliged to respond to the call or text from someone unknown.
And again, should I want to get in touch with someone and I do not have the contact. I ask the middle person to pass my details to the person I wish to reach and tell the topic I want to talk about. You then wait for the person to contact you.
I have been in the situation where people have given my number without my consent. As a result I was talking to someone I did not wish to talk to and spammed later. This is never pleasing to deal with.
Note: this is only advice and a none professional one at that. Should you want to know more do your own research. You can read about the Hong Kong personal date privacy ordinance on the website below. You can also contact aprofessional on that area to answer your questions.
Data Privacy Ordinance link