Pinpoint SMS: Sending SMS (text) messages to India over ILDO

You can use a (unregistered) SenderID for this. It will be random numbers that are sent to handset. However, for this use case, I would recommend a short code because there will be no opt out mechanism for recipients so you should be providing them an alternative way of opting out to be in compliance.

Based on the documentation, here are the key points regarding sending SMS messages to India using Amazon Pinpoint:

By default, Pinpoint uses International Long-Distance Operator (ILDO) routes to send messages to India which have a higher cost. With ILDO routes, recipients will see a random numeric ID instead of your sender ID.

To use a custom sender ID, you need to send messages through local routes instead of ILDO routes. However, to use local routes you must register with the Telecom Regulatory Authority of India (TRAI) which has certain requirements like providing your PAN, TAN, GSTIN numbers.

The registration process allows you to receive an Entity ID and Template ID which must be specified when sending messages locally. This is designed to reduce unsolicited messages and protect consumers.

If sending volume to India is low, using the higher cost ILDO routes is an option without needing India registration. In this case, you can still use a sender ID but recipients will see a random ID instead of your specified sender ID.

https://docs.aws.amazon.com/pinpoint/latest/userguide/channels-sms-senderid-india.html