When you apply for service, you would be given the option to apply for a LifeLine service discount. You MUST qualify for LifeLine to be approved. If you are approved, you would be given a $20 discount off of your phone service. You will get all of the features that any other customer receives, and you will be able to add any add-ons that are available. If for some reason your service is less than $20, you will not get reimbursed, and there will be no buildup of credit. The credit is for the actual service itself.
If you are already a customer and then qualified for LifeLine, you would want to dial 611 to call customer service to get LifeLine added to your account. Remember, LifeLine can only have 1 account to 1 household.