I got one too. I called the number back from a land line phone to complain about them using my text allotment to send me junk. I already have all my phone numbers on the DO NOT CALL registry and I certainly don't want to use my text allotment and iPhone to receive junk!
All I got when I called was a recorded message telling me to check out this website: www.ringcentral.com
Apparently it's a website for a cloud-based phone service. All I can say is if I wanted it, I would look THEM up. They don't need to be forcing their ads on me!