This article addresses what is required to use your existing fax lines with Faxmaker.
FaxMaker is an on-premise software solution and installed in your environment. Your existing fax lines will be routed through your infrastructure from your carrier(s). Your IT group or phone admin with knowledge of your IT and telephony environment will be able to provide the best course of action to complete this. There is no process with GFI that is required.
If more information is required, please see the Determining Ownership of Fax Numbers Used With FaxMaker article.