there are two different issues here. shrinkage (your monthly bill shrinks over time) is done by simply signing up for it.
next is getting cash for referrals which is done by using/giving a code which is sent to a new boost user after the second monthly payment. (not sure how long it takes to get one after doing this). i should be getting a couple of codes within the next 2 to 6 weeks and plan to post them here. remember that you need to keep the account active for a least 2 months for both parties to receive the $25.