When using a trial account with Twilio, all your usage costs are covered by the provided free trial account balance. This includes the one phone number you own as well as any voice calls and SMS messages you make and receive during your Trial period. Learn more here How does Twilio's Free Trial work?

You may notice the billing information on your account's Product Usage page. This is because we want to give you a sense of how much it would cost if you weren't using a trial account. By displaying the amount on your Product Usage page page, we hope to give you a better understanding of our pricing and your own usage.

Since you haven't added any funds to your account, you are not charged for the usage within the provided free trial account balance. In addition, you will not owe for the services used within the provided free trial account balance once you upgrade your account. 

Note: If you use more services than covered by the provided free trial account balance during your trial period, the difference will be deducted from the balance added to the account at the time you upgrade. To learn more see How Twilio billing works.

Once you upgrade your account, then you will be putting money into your account balance. With an upgraded account, any Twilio usage will be deducted from your account balance.