Absolutely, an unsolicited SMS would drive anyone mad, but they're also incredibly low-friction and useful for appointment reminders. Case in point, Ramit Seth

Absolutely, an unsolicited SMS would drive anyone mad, but they're also incredibly low-friction and useful for appointment reminders. Case in point, Ramit Sethi regularly holds one-off sales webinars and ends all (?) of the RSVP ("give me your name and email") funnels with an optional, "Would you like to receive an SMS reminder before the webinar begins?" There's enough of a B2C trust relationship that I don't mind giving up my phone # for a one-time reminder to join the webinars when they begin. It's way simpler than putting a low-priority event like that on my calendar and probably quite effective at converting more people to join the webcast. Compare that to some O'reilly webcasts that advertise via an initial email, have you RSVP by filling out a 7 or 8 field survey, and then still forget to send an email reminder that the webcast is starting. I'm mentally exhausted and I also miss the event.