A2P SMS

Application-to-person SMS: messages sent by software, such as verification codes and alerts, rather than by another person.

A2P traffic is what a platform sends when it texts you a verification code, a delivery alert, or a marketing message. Carriers route and price it differently from ordinary texting between two people, and several countries require senders to register before they can deliver it.

Verification codes are the largest single category of A2P traffic, which is why delivery speed and reliability of these messages vary so much between routes and carriers.

Registration rules that decide delivery

India requires senders to register their names and message templates with the telecom regulator before carriers will deliver their messages, and traffic that does not match a registered template is dropped. The United States runs a similar scheme for business messages sent from ordinary ten-digit numbers, where unregistered traffic is filtered or blocked.

This is why a code from a large local app arrives instantly on an Indian number while a foreign service sending to the same number never gets through.

What it means when you rent a number

You are on the receiving end, so registration is the sender platform's problem rather than yours. What reaches you depends on whether that platform has registered for the destination country and which route it bought.

When a specific service and country pair delivers badly, no amount of retrying on the same pair fixes it, and a different country is usually the faster answer. How an OTP travels follows one message through the whole chain.

What it costs the sender

Verification messages are among the most expensive traffic a platform sends, and the price per message varies by an order of magnitude between countries. That cost is why senders shop for routes, and why the cheapest route often wins inside a company that measures spend rather than delivery.

You see the result as a code that lands in seconds for one service and never arrives for another, on the same number, minutes apart.