Question
Earn DoubleMiles with United's Mileage Plus Visa. To participate in the Double Miles promotion, call 1-800-359-8252 by Sept. 5, to register.
Earn double miles October 31st.
Answer
http://www.flyertalk.com/forum/Forum50/HTML/013153.html
Answer
you can also sign up online at
https://secure.ualmiles.com/VisaRegistration.jsp