Does it cost money to receive calls from gmail?

When logged into gmail, there is the option to “call phone” in the chat window on the left. When you click “call phone”, you can enter a mobile or landline phone number and gmail will call that phone. It is free for the gmail caller.

My question is, does the mobile or landline that you are calling get charged? If it is a mobile that is roaming, do they get charged? If the mobile is not roaming?

I have searched the internet, but cannot find the answer to this very simple question. Anyone have better luck than I?