Is a monthly rate plan mandatory for prepaid account now?

You can change your prepaid plan as you wish to meet your needs, but you have to buy a minimum plan every 30 days to maintain your number, and future connectivity. If you miss payment for 90 days, your number is returned to the pool for reassignment. Prepaid plans can be perfect for folks such as international travellers, who only need cellular service for short periods; there is no long term commitment.