The Phone channel in Freshdesk lets you purchase local and toll-free numbers which your users can call for support.
Your users will be charged when they call your local number (which is available in 36 countries) as per their regular plan tariffs.
Your users will also be able to call the toll-free numbers (available in US, UK, Canada) for which they will not be charged.
However, if they are calling from a different country to a toll-free number, they would have to pay for the ISD call rates.