Twilio Programmable Wireless SIMs are not intended for use in devices that may require emergency calling. End users will be unable to place 911 calls or send 911 SMS messages. As per the Programmable Wireless terms of service, section 7.2, it is the responsibility of the application developer to inform end users that they are prohibited from using Programmable Wireless for placing 911 calls.
The FCC's basic 911 rules require wireless service providers to transmit all 911 calls to a public safety answering point, regardless of whether the caller subscribes to the provider's service or not.
This is why in the United States you can make an emergency call without a SIM card inserted. We can make no guarantees on how our SIMs and emergency calling will work with your phone.
You can find our official position on 911 is described in our terms of service:
There are no exceptions to this at this time. We anticipate delivering a product in the future that is compliant with all relevant 911 regulations and has been technically tested for such support. At such time we will amend the terms of service.