The billing for your subscription begins on the day your number was activated. You will receive your first invoice at the beginning of the next month, on which you will be billed partially for the current month (from the day your number got activated until the end of the month) as well as for the following month.
Example: My subscription has been active since the 15th of September. My invoice at the beginning of October will be as follows:
– Subscription invoiced from 15 to 30 September prorated to the number of active days: 16 days out of 30
– Subscription invoiced from 1 to 31 October: 31 days