Whatsapp Business Phone portability rules
A phone number already being used with the WhatsApp Business API cannot be migrated. Your client must obtain/use new phone number(s) to register WhatsApp to register it to the WhatsApp Business API.
You may use a phone number that is already registered in the SMB/Consumer App (Android, iPhone or Business Application versions of WhatsApp). However, if you try to add that phone number to your Business Manager, you will see a Phone Number Is Invalid error. First, you have to delete the old WhatsApp account associated with that phone number before creating a new one on the WhatsApp Business API.
Short codes are not allowed on the WhatsApp platform. Land lines are acceptable phone numbers to use. The number must include a country and area code. Since a phone number is tied to a WhatsApp account, you must own this number.
Any phone number the business wants to register on WhatsApp needs to be able to receive an SMS or phone call (from US phone number) to get the registration code.
Once you register a phone number with the WhatsApp Business API, it cannot be used for any other WhatsApp client (no downgrade).
Toll free numbers
Businesses want to use phone numbers their customers already know, such as their 1-800 or other toll-free number. These numbers areusually behind an IVR, which a WhatsApp registration call
Instead, WhatsApp is able to share with you 1 to 2 phone numbers thatthe registration phone call will comefrom. You can use this information tocreate a whitelist for those numbersso that once the call comes in, you can redirect it to an employee or mailbox where the registration code will be captured.