Ask HN: How do your customers contact you by phone?

Do you still talk to your customers on the phone? Do they call your landline or cellphone? Do you use a phone system, voicemail, concierge service or do they call you directly? Do you offer a toll free number?

I am working on a new business phone service ( https://www.clinq.app/en/ ) and I would like to know more about the phone habits of international businesses.