Although many Twilio customers permit their end customers to port away Twilio phone numbers from the Twilio platform, you should determine this issue with your legal counsel.  In particular, many Twilio customers permit their end customers to port away phone numbers under the following circumstances:

• Your end customer has been assigned or purchased a specific phone number, pays for the use of that phone number, and is the party that answers the phone number whenever the number is called.
• Prior to signing up for your service, your end customer used the phone number and then ported the phone number into your Twilio project.
• Twilio uses an unauthorized porting procedure to prevent the number from being released by notifying the authorized user if the end user contacts them to port away the number. 

Unauthorized Port Away requests: 

Sometimes, end users will reach out to Twilio requesting customer service records (CSR) information.  Even though they use the numbers, Twilio does not consider them as the authorized users. Hence, Twilio reaches out to their customers listed under their records and informs them about the request.

Twilio provides 5 business days to get a response from the authorized user and provides the port-away information post the mentioned time as per the FCC regulatory guidelines. 

Note: It is recommended for the end users to reach out to their resellers or providers for the port-away information. To obtain port information and prevent any unwarranted requests, this is the simplest method.