Upcoming changes to <Dial> verb URL parameter behavior

On 1 July 2021 we will make a change to the list of TwiML verbs that are allowed to be returned in the url parameter of <Dial> nouns.

The TwiML <Number>, <Client>, <Queue>, and <Sip> nouns allow developers to provide a url parameter that will execute when the called party answers. The url parameter is typically used as a call screening option to <Play> or <Say> notifications to callers about the incoming call, or <Gather> is used to retrieve input from the called party before bridging the calls.

We are making a change to prohibit the execution of any <Dial> verbs returned by the noun url instruction. Returning a <Dial> verb in the noun url can result in costly call loops that result in significant billed usage on the account.

We are unaware of any valid use cases for this behavior, but we are publishing this changelog in the spirit of no shenanigans.