How fast can I place or receive phone calls with Twilio? – Twilio Support

Question

How fast can I place or receive phone calls with Twilio?

Product

Programmable Voice

Answer

There are some limitations to the number of simultaneous inbound and outbound calls that can be placed and received using Twilio's Programmable Voice, Client, and Elastic SIP Trunking products. This guide explains the restrictions for these products.

Call Concurrency Limitations

Trial Account:

Programmable Voice = 5

Elastic SIP Trunk = 4

Upgraded Account with an approved Individual PCP:

Programmable Voice = 10

Elastic SIP Trunk = 10

Upgraded account with an approved Business PCP:

Unlimited for both Programmable Voice and Elastic SIP Trunk

Outbound SIP and API request calls

By default, each Twilio account can make 1 outgoing call per-second (CPS). This rate limit applies to both Outbound API-requested Programmable Voice calls, and Elastic SIP Trunking calls. You can have as many concurrent calls as your servers will allow (with an approved Customer Profile), but calls can only be placed at the rate of one per second.

Notice: API requests for calls that exceed the CPS rate limit will be queued, and executed as capacity is available. Calls that exceed 24 hours in the queue will be cancelled. Exceeding the CPS rate on an Elastic SIP Trunk will result in a failed call with a SIP 503 Trunk CPS limit exceeded response.

Notice: In aggregate calls are executed at the rate defined by the CPS. Individual calls may not execute at the anticipated rate — you may see individual seconds with more or fewer CPS, especially for bursty traffic — but over a month the call execution rate will average the CPS rate set for that account or trunk.

If your project requires additional outbound call throughput, you can increase your CPS limit from Twilio Console:

Programmable Voice and Client: Set CPS in the "Calls per Second" section on the Voice Setting page.
Elastic SIP Trunking: Set CPS per region in the "Calls per Second" section of your trunk's Termination settings page.

Outbound <Dial> calls

There is no rate limit for outgoing <Dial> calls for forwarding, conferencing, or Client (with an approved Business PCP ). That said, there are limitations at the destination for these calls:

Twilio <Dial> forwarding to another phone number limitations depend on the destination phone number. Calls exceeding the limit may not connect or be marked busy.
Twilio <Conference> has a maximum limitation of 250 participants, but rooms can be configured to have a lower maximum.
Twilio <Client> calls forwarded to a user who is already connected will fail with a SIP 486 Busy here response.
Twilio <Client> calls toward an endpoint that is not registered/online will result in SIP 410 Gone response.

Incoming calls

Twilio places no limitations on the rate at which projects can receive inbound calls (with an approved Business PCP ). Every incoming call received at your Twilio phone number corresponds to an HTTP request we submit to your webhook / request URL or SIP Trunk Origination URI. We recommend users make sure your server is capable of handling the load if you are expecting a large amount of concurrent inbound traffic.