When your account balance reaches zero you will no longer be able to make and receive phone calls or send and receive SMS messages. You won't lose your phone numbers right away.
We will continue to bill your account for 60 days for the phone numbers you've purchased. If you pay off your balance and fund your account with a minimum of $20, you’ll be able to use your phone numbers again. After 60 days, if you haven't replenished your Twilio account balance, we may close your account and return your phone numbers to our pool of available numbers.