It's awesome that we can now associate multiple numbers with a contact! Below are some enhancements that would be nice to see moving forward:
Filter on additional numbers in smartlists like we can with emails.
Phone number label customization.
Ability to add the same label to multiple numbers (ex: 3 mobiles and 2 landlines)
Ability to interact with additional numbers via workflow and API
Ability to change primary number via workflow and API
Ability to text multiple numbers for a contact at one time