You can only have multiple numbers under one account with Fongo Works.
All other Fongo services (Home Phone, Mobile, FreePhoneLine) can only have one number per account. If you're looking to utilize more numbers for the same service, you will need to register for another account using a different email address.
For example, you may have 2 Fongo Home Phone numbers but with the emails myemailforFongo001@email.com and myemail1forFongo002@email.com.