You certainly do not need a MANDATORY mobile number to sign up. Some do not have a mobile phone for one thing. For another it is a definite trap to actually having an account compromised BY YAHOO! if (and inevitably WHEN) someone gets a new mobile number. I KNOW. B/C Facebook had a similar TRAP whereby I was denied access to my own account b/c the mobile number I signed up with no longer existed. BUT 'they' INSISTED I send a message from THAT number. They would NOT acknowledge my messages that I no longer had that mobile number. And, therefore, I was sabotaged out of that F.B. account. I learn from experience what works and DOES NOT WORK. Please do the same and stop harassing your clients with absolutely unnecessary power control. The more you 'enhance security' the less security we really have. (just the way it is) Thank you for listening and heeding what is a definite necessity on your part to remove this dictatorial mandate to having a mobile number listed. I'm sure the NSA can find other silent weapons for there espionage on innocents!