I am trying to activate that as we speak, but I never get the SMS. I tried 6 times in the last 3 hours. I guess it's overloaded or broken at least for my phone number (german mobile phone).
All I can suggest is to keep trying every few months. I have been trying for years. My carrier still isn't listed but it finally started working about two weeks ago for me (I'm not in Germany though). Now I have to hope it keeps working with my still unlisted carrier or I risk getting locked out of my account. At least the bad guys are locked out too...