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Best Practices for Voice Calls Trusted Communication

Maintaining consumer trust in the voice communication channel is critical. Consumers expect to receive wanted and personalized communications, while being protected from spam and unwanted calls. This guide provides best practices to ensure your voice communications are safe, wanted and legal.


Twilio’s Acceptable Use Policy (AUP) outlines the rules for using Twilio’s products, and services. It’s vital that all customers know and understand the AUP, and conform to the rules and regulations within it to prevent actions that are not allowed or illegal. For full details, please see Twilio's Acceptable Use Policy.

Twilio Voice Services Policy

Twilio’s Voice Services Policy provides the restrictions and requirements you must abide by in order to use Twilio’s Programmable Voice and Elastic SIP Trunking (collectively “Twilio Voice Services”) This policy is part of Twilio's Acceptable Use Policy, which we encourage you to read. For full details, please see Twilio Voice Services Policy.

Trust Hub

Twilio provides Trust Hub as a resource to engage with our customers to build trust within the telephony ecosystem. By registering in Trust Hub, our customers are able to experience increased voice call deliverability rates and higher call answer rates. Trust Hub allows customers to register their business profile, including Know Your Customer (KYC) information.

All Twilio customers using communication products must create Primary Customer Profiles in Trust Hub. The profile is used to establish the reputation of your calls, is a prerequisite for enabling advanced trusted calling capabilities, and is used as a reference to help resolve any compliance issues you may have on your account (e.g., an established customer profile can be used to more quickly resolve fraud investigations as the profile identity is known).
Please note, in order to make outbound calls to the US and Canada, it is required you have an approved Primary Customer Profile otherwise your call can be blocked (see error code 21216). 

Trust Hub Products for US Calling

  • SHAKEN/STIR: Increase trust in your calls by displaying a trust indicator like "Caller Verified” on the called party’s phone
  • Voice Integrity: You can register your Twilio phone numbers via Trust Hub, which will then register them with the analytic engines responsible for running spam labeling algorithms on AT&T and T-Mobile. (Verizon support to be added in the future)
  • Caller ID Name (CNAM): Display the name of your business on the called party’s phone using Caller ID Name (CNAM) service
  • Branded Calls:Branded Calling is a Voice Trust Product that enables our customers to provide a Display Name on any terminating handset (no app required) when outbound calls are made from Twilio numbers.

For full details, see our Trust Hub documentation.

Caller Reputation

With spam calling on the rise, there is continued scrutiny of voice calls in the industry and increasing call screening and spam blocking efforts. To help improve your answer rates, Twilio has compiled this list of recommendations and best practices to maintain a positive caller reputation, and avoid being labeled as spam. For full details see our guide Recommendations and Best Practices for Maintaining a Positive Caller Reputation.

Responsibility of Independent Software Vendors (ISV)

If you are an Independent Software Vendor (ISV) - a Twilio customer who uses Twilio services in the delivery of your services to your own customers that means it is your responsibility to adhere to our policies and that extends to the activity of your customers. It is especially important for ISVs to have systems in place to continuously monitor their customers’ activities (e.g. call metrics, answer rate, review of voice calls campaigns, etc.) to detect, isolate and immediately remediate all illegal activity and unwanted communications.

To and From number

The phone numbers for all calls terminating to the PSTN must be in E.164 format as this allows phone calls and text messages to be correctly routed to individual phones in different countries. E.164 is an international standard, titled The International Public Telecommunication Numbering plan, that defines a numbering plan for the worldwide public switched telephone network and some other data networks. E.164 defines a general format for international telephone numbers. For full details see Twilio prioritizes national routes so that the calling number is displayed in National format and not in E.164 format.

In an outgoing call initiation, the from number is required to be a Twilio number owned by the Twilio account, or a Verified Caller ID in the account. For more information about how to format the to and from numbers for your Twilio calls, please see our guide Simple Example for Placing Programmable Voice Calls.

International calling and usage

It is a good practice to check regulatory guidance in your and your end users jurisdiction prior to generating voice calls. Every country has the right to regulate and build a public telephone network that meets the needs of its citizens. So it is not surprising that nuances exist from one country to the next, and from one carrier to the next.

The following references can serve as a guide: International Voice Quirks. To see country by country nuances see the Voice Guidelines and Phone Number Regulations. Please note regulatory changes are fluid and subject to change.

Toll-free phone number restrictions and limitations

Toll-Free numbers are designed to be used for domestic inbound voice calls, and have many unique requirements and characteristics that should be considered before purchasing one of these numbers. For example, using a Twilio Toll-free number as the from number is not supported. Carriers do not expect Toll-free numbers to be used on outbound calls and as a result these calls may fail.

For full details, see our article Toll-free phone number restrictions and limitations.

Voice call troubleshooting

This is an index of some common issues, and steps to troubleshoot them: Troubleshooting Voice Calls

Voice Insights

Voice Insights offers a transparent view of how your calls are performing, giving users access to analytics to help identify trends, and diagnose potential issues. The Basic offering has the Call Summary tab on your calls to see details like the carriers used, last SIP response, post-dial delay (PDD), media latency, verified callers, and who hung up. The paid Advanced version shows SDK eventing, metrics, and network performance graphs and exposes an API.

For full details, see Getting Started with Voice Insights and Voice Insights Advanced Features.

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