Rules for posting contacts on the site, convenience for visitors. To be honest, there are no clear restrictions on this. But often when you go to some resources you have difficulty finding a button to call or write to the messenger.

My vision and not only this, the user should simply click on the phone or a similar icon, and he will immediately dial the desired number on his mobile phone. Or he can send a message via email, Viber, Telegram, WhatsApp and more. Moreover, contact information can be duplicated at the bottom of the site; often there are links to social networks, absolutely true. And for shops there must be a map, unless of course you can enter it from the street.

If the resource menu at the top is motionless when scrolling, it should contain contact information, a visitor in the 21st century is not ready to spend a lot of time searching. Moreover, if the site has a sidebar (column on the right or left), you can also place some of your contacts there. Especially with long pages. 

Some people believe that a pop-up chat window with support will replace duplicating contact information. Personally, it sometimes annoys me a lot. similar window popping up like I am your manager. I think this communication scheme is more suitable for online stores, although if we take the most famous ones in Ukraine, then there is no more than yes.