What Are A2P SMS Routes? Direct vs Grey Routing Explained

Two suppliers quote the same destination at the same rate. One delivers ninety-something per cent of your OTP traffic inside ten seconds with your brand name on it. The other delivers a number that looks similar on a dashboard while your support queue fills with users who never got the code. The rate sheet did not distinguish between them. The route did.

What an A2P SMS route actually is

An A2P (application-to-person) SMS route is the path a message takes from your platform to a subscriber handset. It usually involves your platform, an aggregator, one or more interconnects, and the destination operator’s SMSC. Every hop on that path is a place where the message can be delayed, filtered, stripped of its sender ID, or acknowledged as delivered when it was not.

The word “route” is doing a lot of work in a rate sheet. It can describe any of the following, and suppliers are not always careful about which.

Direct, transit and grey routes

Direct operator routes. Your supplier has a commercial interconnect with the destination operator. Traffic is billed, sender IDs behave as registered, and delivery receipts reflect handset delivery. This is the expensive option and the one that survives regulatory attention.

Transit routes. Traffic reaches the operator through one or more intermediate aggregators. This is legitimate and extremely common, most global coverage is built this way. The trade-off is that every hop adds latency, another party who can mishandle your sender ID, and another place your delivery receipt can be generated rather than relayed.

Grey routes. Traffic reaches the handset through a path the operator has not authorised and is not billing for, typically SIM banks or an international interconnect being abused for domestic termination. It is cheap. It is also unstable by design: operators actively hunt these paths, and when one closes your traffic stops mid-campaign, frequently taking your sender ID reputation with it.

How to tell which one you have

Ask, and see whether you get a straight answer. Beyond that, four practical tests:

• Send to your own handset. Does your registered sender ID arrive intact, or has it been replaced with a random long number? Replacement is a strong grey-route signal.
• Compare submit time to receipt time. If receipts return in under a second, they are almost certainly generated on submission rather than on delivery.
• Test at local peak. Grey routes and thin transit paths degrade sharply during the destination’s evening peak. A route that only performs at 4am is not a route you can build on.
• Ask what happens when it breaks. A supplier with a real interconnect can tell you which operator, which standby route, and what the failover behaviour is. A supplier without one will talk about “our network”.

Why the cheap route is usually more expensive

Price per message is the wrong denominator. The one that matters is cost per delivered message, and for OTP traffic, cost per verified user.

Work it through: a route at twenty per cent below market that delivers eighty-five per cent instead of ninety-five is already close to break-even on cost per delivered message. Add the users who abandoned signup because the code arrived after they gave up, the support tickets, and the day of lost traffic when the route closes without warning, and the saving has been gone for some time.

What to ask a supplier before you buy

1. Is this destination direct or transit? Which operators?
2. Are delivery receipts end-to-end, or generated on submission?
3. What are the sender ID rules here, and do you handle registration?
4. What is the standby route if the primary degrades, and does failover need a ticket?
5. How does this route behave at local peak?

A supplier who answers all five specifically is worth testing. One who answers none of them specifically is selling you a rate, not a route.

Where this leaves you

Use direct routes for anything time-critical or brand-bearing: OTP, transaction alerts, anything where a failure is a lost customer rather than a lost impression. Use transit routes where coverage matters more than the last few points of delivery. Do not use grey routes at all, and be suspicious of any quote that only makes sense if someone is.

Our A2P SMS routing page states the routing type per destination, and the coverage table records the sender ID rule for each market.