Adding this Phab as discussed w/ @Lars & @Eileenmcnaughton -- we are in need of an automated way to opt users into the SMS program in Acoustic via the paymentswiki &variant=smsOptin form, which triggers a legally-required welcome message and enables users to receive broadcasts.

Acoustic's Transactional SMS REST API documentation is here
Message users would need to receive on signup is:

Wikimedia: You have successfully opted-in to receive text updates. Message & data rates may apply. Message frequency varies. Reply HELP for help, STOP to quit.

Acoustic Campaign name: "Two-Way Opt-In"
Acoustic Campaign ID: af111b1f-bc8b-4edc-a743-408594312f99

Happy to find more Acoustic field names, etc. that we may need or help test w/ a US phone number.

Thanks!
Sean