Outbound agents and premium-rate numbers: the pumping problem

Some phone numbers earn money when they receive a text or a call. Premium-rate numbers are the obvious case, but the larger one is ordinary numbers on expensive international routes, where the carriers along the way split the termination fee. A fraudster who controls such numbers, or has a deal with a carrier that does, makes money every time someone else's system texts or calls them.

Pumping is getting your system to do that, thousands of times. You pay the sending cost. They take a share of it. The texts and calls themselves are worthless; the traffic is the product.

The classic target is any form that sends a text to a number the visitor types in: sign-up verification codes, password resets, "text me a link". A script fills the form over and over with numbers on expensive routes, your system dutifully sends a code to each, and nobody ever enters one.

The tell is in the numbers: a sudden rise in texts to countries you don't do business in, destination numbers that run in sequence, and verification codes that are almost never used.

An AI agent that can send texts or place calls is the same form, with a friendlier interface. Anything that lets the conversation decide which number gets dialed or texted is a way in:

• "Text me the confirmation at" followed by a number the caller reads out.
• "Can you transfer me to my colleague at" followed by a number on an expensive route.
• "Call me back on this number instead."
• An outbound campaign fed by a list or a web form nobody checked.

A person on the phone would find a caller asking to be transferred to a number overseas odd. An agent built to be helpful will simply do it, and do it for every caller who asks the same way.

• Never let the conversation choose a destination. Transfers go to a fixed list of your own numbers. Confirmations go to the number the caller is calling from, or to one already on their account.
• Turn off the countries you don't serve. Carriers let you restrict where your account can call and text; on Twilio, that's Voice Dialing Geographic Permissions and Messaging Geographic Permissions. If you only serve the US and Canada, allow only those.
• Block premium-rate and high-cost ranges outright, even inside countries you do serve.
• Limit per caller and per destination: no single caller should be able to trigger more than a couple of texts, and no destination should receive more than a handful a day from you.
• Put a check in front of sign-up codes, and turn on the fraud screening your verification provider offers.
• Watch where your outbound traffic goes. The pattern (new countries, sequential numbers, codes nobody uses) is visible in your logs well before it shows up on the bill.

This is one line in the pre-launch checklist, and one of the reasons the never-do list includes "never dial or text a number the caller supplies".