You cannot purchase toll-free numbers directly in turboDial.
However you can purchase them in Twilio and then move into your turboDial account. Use steps 2 and 3 of the number porting instructions.
You can use this approach to acquire any type of number that is available from Twilio. Acquiring numbers directly in turboDial is the best approach, but in some cases you may find numbers via your Twilio account that you were unable to find in turboDial.
In a similar manner, if you have a toll-free number as part of another service, you can port it to Twilio and then transfer it to turboDial, using the same steps used for a traditional number.