Just like T-Mobile's "Fav-Five", sprint has a $5/month addon called "Pick Three". You can have three phone numbers (domestic, lanline, cell, other cell provider) at one time. This is for in and outgoing calls. You can swap the three numbers out as much as you want via phone CS as well!

Just call CS and as for the Sprint Big Three. If you contact ecare via online chat they will tell you to call CS.

I am getting this added to my account right now as i type!

ENJOY!