Porting a number simply refers to the process of taking an existing active business phone number (Local or Toll-Free) from the current provider and transferring it to a new service provider. Providers may have different requirements for porting a number, but on average expect a number to be ported between 7 and 10 business days.
To port a number, make sure to include a LOA (Letter of Authorization). To see a sample of this go to Help & Support > Reseller Portal > Local 10-Digit Long Codes (10-DLC) & Toll-Free Numbers > LOA (Letter of Authorization)