Step 1*

SketchSystems.spec

Step 1*
  mobile number form*
    submit -> verify mobile number
  verify mobile number
    api error -> mobile number error
    done -> Step 2
  mobile number error 
    try again -> Step 1

Step 2
  activation code form*
    submit -> verify activation code
    request new code -> verify mobile number
  verify activation code
    api error -> activation code api error
    code error -> activation code error
    done -> Step 3
  activation code error
    try again -> Step 2
  activation code api error
    try again -> Step 2

Step 3
  email address form*
    submit -> confirm email address
  confirm email address
    edit -> email address form
    confirm -> register user
  register user
    new user -> newly registered user
    existing user -> already registered user
    api error -> email address error
  email address error
    try again -> Step 3

Done
  newly registered user
  already registered user