Instead they bought API access without the leastest of due diligence, putting their customers and their reputation at risk.
Additionally, the merging of different customer’s data by the processor is probably not GDPR-compliant (even if access control was in place).
Isn't the hard prt the connectivity bit i.e. negotiating with the various telcos? I once saw a telco use a third party SMS vendor for messaging their own customers for an app - because setting it up internally was too much of a hassle.
We connected to multiple aggregators. It's been a few years, but the big players in the US (Verizon, AT&T, Sprint, T-Mobile) were split between different aggregators. It was a similar situation in Europe.
A big part of working with a new aggregator was a full review of security and privacy, and that became even more important as we began the process of being acquired by an F100 company.
I'm still trying to figure out why messages were stored in S3 buckets to begin with. That's an architecture choice that makes little sense to me, especially since the limited size of SMS makes them pretty space efficient.
GDPR is not necessary applicable here. An SMS gateway is most likely classified as a telecom carrier, and thus any local telco laws would be applicable and not GDPR. That applies only to the transfer of the SMS though, so for example a customer GUI of sent SMS would be out of that scope.
(And before someone tells us that SMS 2FA is insecure I would like to point out that we use this for verification purposes in our booking system when a customer makes a booking. So for end-customers, not for users. It is a chosen strategy for making verification easy as alternatives are too complex for many consumers. All users however authenticate with email and password, and have the option of adding TOTP 2FA).
Apart from that, to me it seems justifiable to follow a risk based approach. Booking systems up to a certain value/amount, fine. Online Banking and health related services, thank you, no.
For signups to our app (to get an account with a booking site) we require a password.