Why is my invoice pro-rated?
Your first invoice is pro-rated from the day of sign up to the last day of the month. This includes your minute plan. If you signed up halfway through the month, then your first month minute plan would allow for half of the minutes.
Formula for calculating pro-rated plan minutes:
Pro-rated plan minutes = (Plan Minutes / Number of days in the month) x (Number of remaining days in the month after sign up date)
The total invoice would be pro-rated plan charges + overages (if any) + additional charges (if any).