TwiMLTM Voice: <Number>

The <Dial> verb's <Number> noun specifies a phone number to dial. Using the noun's attributes you can specify particular behaviors that Twilio should apply when dialing the number.

You can use up to ten <Number> nouns within a <Dial> verb to simultaneously call all of them at once. The first call to pick up is connected to the current call and the rest are hung up. For each <Number> noun you can specify what call progress events you want to receive webhooks for.

Noun Attributes

The <Number> noun supports the following attributes that modify its behavior:

Attribute NameAllowed ValuesDefault Value
sendDigitsany digitsnone
urlany urlnone
methodGET, POSTPOST
statusCallbackEventinitiated, ringing, answered, completednone
statusCallbackany urlnone
statusCallbackMethodGET, POSTPOST

Phone numbers should be formatted with a '+' and country code e.g., +16175551212 (E.164 format). Twilio will also accept unformatted US numbers e.g., (415) 555-1212 or 415-555-1212.

sendDigits

The 'sendDigits' attribute tells Twilio to play DTMF tones when the call is answered. This is useful when dialing a phone number and an extension. Twilio will dial the number, and when the automated system picks up, send the DTMF tones to connect to the extension.

url

The 'url' attribute allows you to specify a url for a TwiML document that will run on the called party's end, after she answers, but before the parties are connected. You can use this TwiML to privately play or say information to the called party, or provide a chance to decline the phone call using <Gather> and <Hangup>. The current caller will continue to hear ringing while the TwiML document executes on the other end. TwiML documents executed in this manner are not allowed to contain the <Dial> verb.

method

The 'method' attribute allows you to specify which HTTP method Twilio should use when requesting the URL in the 'url' attribute. The default is POST.

statusCallbackEvent

When dialing out to a number using <Dial>, an outbound call is initiated. The call transitions from the initiated state to the ringing state when the phone starts ringing. It transitions to the answered state when the call is picked up, and finally to the completed state when the call is over. With statusCallbackEvent, you can subscribe to receive webhooks for the different call progress events: initiated, ringing, answered, or completed for a given call.

The statusCallbackEvent attribute allows you to specify which events Twilio should webhook on. To specify multiple events separate them with a space: initiated ringing answered completed. If a statusCallback is provided and no status callback events are specified the completed event will be sent by default.

The initiated, ringing, and answered events have a cost of $0.0001 per event, which results in $10 for every 100,000 events. The completed event is not charged.

As opposed to creating an outbound call via the API, outbound calls created using <Dial> are initiated right away and never queued. The following shows a timeline of possible call events that can be returned and the different call statuses that a <Dial> leg may experience:

Outbound Dial call events diagram

EventDescriptionCost
initiatedThe initiated event is fired when Twilio starts dialing the call.$0.0001 per event
ringingThe ringing event is fired when the call starts ringing.$0.0001 per event
answeredThe answered event is fired when the call is answered.$0.0001 per event
completedThe completed event is fired when the call is completed regardless of the termination status: busy, canceled, completed, failed, or no-answer. If no statusCallbackEvent is specified, completed will be fired by default.No cost

statusCallback

The statusCallback attribute allows you to specify a URL for Twilio to send webhook requests to on each event specified in the statusCallbackEvent attribute.

statusCallbackMethod

The statusCallbackMethod attribute allows you to specify which HTTP method Twilio should use when requesting the URL in the statusCallback attribute. The default is POST.

Status Callback HTTP Parameters

The parameters Twilio passes to your application in its asynchronous request to the StatusCallback URL include all parameters passed in a synchronous request to retrieve TwiML when Twilio receives a call to one of your Twilio numbers. The full list of parameters and descriptions of each are in the TwiML Voice Request documentation.

When the call progress events are fired, the Status Callback request also passes these additional parameters:

ParameterDescription
CallSidA unique identifier for this call, generated by Twilio. You can use the CallSid to modify the child call by POSTing to Calls/{CallSid} with a new TwiML URL.
ParentCallSidA unique identifier for the parent call.
CallStatusA descriptive status for the call. The value is one of queued, initiated, ringing, in-progress, busy, failed, or no-answer. See the CallStatus section for more details.
CallDurationThe duration in seconds of the just-completed call. Only present in the completed event.
RecordingUrlThe URL of the phone call's recorded audio. This parameter is included only if Record=true is set on the REST API request and does not include recordings from <Dial> or <Record>. RecordingUrl is only present in the completed event.
RecordingSidThe unique ID of the Recording from this call. RecordingSid is only present in the completed event.
RecordingDurationThe duration of the recorded audio (in seconds). RecordingDuration is only present in the completed event.
TimestampThe timestamp when the event was fired, given as UTC in RFC 2822 format.
CallbackSourceA string that describes the source of the webhook. This is provided to help disambiguate why the webhook was made. On Status Callbacks, this value is always call-progress-events.
SequenceNumberThe order in which the events were fired, starting from 0. Although events are fired in order, they are made as separate HTTP requests and there is no guarantee they will arrive in the same order.

Examples

Example 1: Using sendDigits

In this case, we want to dial the 1928 extension at 415-123-4567. We use a <Number> noun to describe the phone number and give it the attribute sendDigits. We want to wait before sending the extension, so we add a few leading 'w' characters. Each 'w' character tells Twilio to wait 0.5 seconds instead of playing a digit. This lets you adjust the timing of when the digits begin playing to suit the phone system you are dialing.

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Dial>
        <Number sendDigits="wwww1928">
            415-123-4567
        </Number>
    </Dial>
</Response>

Example 2: Simultaneous Dialing

In this case we use several <Number> tags to dial three phone numbers at the same time. The first of these calls to answer will be connected to the current caller, while the rest of the connection attempts are canceled.

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Dial>
        <Number>
            858-987-6543
        </Number>
        <Number>
            415-123-4567
        </Number>
        <Number>
            619-765-4321
        </Number>
    </Dial>
</Response>

Example 3: Call Progress Events

In this case we want to receive a webhook for each call progress event when dialing a number using <Dial>.

<?xml version="1.0" encoding="UTF-8"?>
<Response>
        <Dial>
                <Number
                 statusCallbackEvent="initiated ringing answered completed"
                 statusCallback="https://myapp.com/calls/events"
                 statusCallbackMethod="POST">
                        +14158675309
                </Number>
        </Dial>
</Response>

Example 4: Multi Dial with Call Progress Events

In this case we want to receive a webhook for each call progress event for each number when dialing multiple numbers using <Dial>.

<?xml version="1.0" encoding="UTF-8"?>
<Response>
        <Dial>
                <Number
                 statusCallbackEvent='initiated ringing answered completed'
                 statusCallback='https://myapp.com/calls/events'
                 statusCallbackMethod='POST'>
                            +14155555555
                </Number>
                <Number
                 statusCallbackEvent='initiated ringing answered completed'
                 statusCallback='https://example.com/events'
                 statusCallbackMethod='POST'>
                            +14153333333
                </Number>
    </Dial>
</Response>

Hints and Advanced Uses

  • You can specify up to ten numbers within a <Dial> verb to dial simultaneously
  • Simultaneous dialing is useful when you have several phones (or several people) that you want to ring when you receive an incoming call. Keep in mind that the first call that connects will cancel all the other attempts. If you dial an office phone system or a cellphone in airplane mode, it may pick up after a single ring, preventing the other phone numbers from ringing long enough for a human to ever answer.

    Hence you should take care to use simultaneous dialing in situations where you know the behavior of the called parties.