The amount that was added to a user's account, prior to sending someone an SMS, through a top-up is the sole amount from which he or she can send an SMS. In the Shared Package, the charges for sending an SMS vary, and it directly depends on the top-up amount which the user purchased. It is well explained in the pricing section. Charges will be deducted from the balance in accordance with the characters of the SMS, as one SMS is comprised of 160 characters.