Automated SMS steps in sequences are carried out automatically and, by default, include the validation of contact phone numbers. This process lets us distinguish valid from invalid numbers and, among them, detect phone number types. After validation, our system sends auto SMS only to valid and mobile phone numbers. As a result, you can be sure that messages are sent to the recipients that can potentially receive them, which improves message deliverability.

Why is phone number validation important?

Among all cases when SMS cannot be delivered, there may be an invalid phone number, which means that it was entered incorrectly or does not exist, or a landline phone number type.

Sending SMS is impossible in those cases, but the system may still try to send messages, and you risk facing delivery errors and unclear statistics on the sent SMS. When we verify a phone number, it improves how the SMS is routed, and we make sure it gets to the right place.

How the validation of phone numbers works

We use the Twilio Lookup API to check all the phone numbers linked to the contact profiles. After validation, the system receives the types of phone numbers and then processes those phone numbers according to their types.

Possible results of the validation are valid, invalid, and unknown. Here's a full overview of how it works:

Status of phone numbers


Action with auto SMS

Valid + phone number type is mobile

The entered phone number is correct.

As mobile phone number type, a system recognizes mobile, fixed VoIP, non-fixed VoIP, personal, tollFree, premium, shared-cost, uan, or pager phone numbers.

Auto SMS will be sent.

After the validation, an icon of a phone will be shown near a contact's number in a people list and in the sidebar in the phone field.

Valid + phone number type is Landline

The entered phone number is correct, but messages cannot be sent to it.

As a landline phone number type, a system recognizes landline, voicemail, and pager phone numbers.

Auto SMS will not be sent.

The status of contact in the sequence is "Missing data."

An icon of a house will be shown near a contact's number.


The phone number is missing or has been entered incorrectly.

Auto SMS will not be sent.

The status of contact in the sequence is "Missing data."

An icon of an invalid phone number will be shown near a contact's number.


The phone number is entered correctly, but we cannot check whether it is a mobile or landline number due to a lack of information from the carrier.

We send SMS anyways.


  • Validation of phone numbers is processed automatically and is required for the AutoSMS step in the sequence.

  • Reply checks phone numbers from all countries except Canada. Because Canadian law protects personal information, it is not possible to access Canadian phone numbers with additional applications. We do not guarantee delivery to Canadian numbers.

  • Each phone number is validated only once, then the system stores the record with its status and the number will be processed in all further campaigns according to it.

  • Once you change or edit the phone number in the contact's profile, it will be validated again.

  • If Lookup is not available (the server doesn't respond), an SMS will be sent without validation.

Validation pricing

Validation only works after payment has been made.

Reply charges you $0.008 from your wallet per validation of one phone number. Validation works per request, which means you pay only when you use it. This price is determined by Twilio's pricing (Line Type Intelligence tariff).

Did this answer your question?