(I suppose if you just want some email address, not specifically Yahoo, you could just create a gmx.com (or other) account and stop there.) On I created one successfully with gmx.com which does not require a mobile number. Now, of course, you need another email address that itself doesnt require a mobile number.
On the sign up page, click on 'I'd rather use my own email address.' You can create (or, more specifically, I was just able to create) a Yahoo account without a mobile number by signing up with an existing email address.
