I would like to understand what would be my best plan option for roughly around 40-50k minutes a month. Im currently in the Ad-hoc, but whenever I use the calculator from Vapi to simulate my cost, Ad-hoc is always a cheaper cost than startup, for example. Does this qualify for enterprise? What would be the advisable plan?

The best option is to choose the growth plan, which offers an overage cost of 14 cents per minute and provides 1000 concurrent lines to help you grow significantly. For now, consider starting with the small plan and then scaling up as you approach the limits.