How does Twilio bill me?
As you use Twilio services (minutes, SMS messages, phone numbers, transcriptions, etc.) we draw down your account balance. When your account reaches $0, we will suspend your account. Don’t worry, we’ll notify you by email when your balance hits $10 and again when your balance reaches $0.
On your billing page, you can manually recharge, or have us automatically recharge your balance when it falls below a chosen threshold.