What are credits and credit balances?

 If a user is enrolled in the Monthly Subscription plan, they may be asked to “add credits to the credit balance”. So, what are credits and what is the credit balance?
Credits are units applied in U.S. dollars to the account balance. Credits are required for purchasing the services and items with Silent Circle. These services include the monthly subscription fee of $9.95 for unlimited global calling, texting and video calling to other Silent phone users. Credits are also used for purchasing a Silent Circle telephone number and when making calls to non-silent circle contacts such as landlines and cellular numbers (when available). When consumed, credits are deducted from the Credit Balance.
The credit balance is the pool of credits attached to each Monthly Subscription user account. The credit balance is maintained by the user. A credit card is required to apply credits to the account. However, it is up to the user to apply sufficient credits to maintain monthly subscription costs and Silent World calling consumption. Silent Circle will not automatically bill the credit card on file to renew services. If the credit balance falls below the monthly subscription cost, the system will suspend the account until credits are added