This is the key point isn't it? For so many services whose core demographic is not HN readers, vast numbers of the customers will prefer to use a telephone over anything else. Even I will occasionally prefer to call if there's an issue with a large company that needs sorting immediately, or I'm finding emails getting constantly ignored.

Certainly requiring a telephone number (or any other personal details that I'd rather not share) is ridiculous, and it's the company's responsibility to contact me at my convenience, but there'd be a far bigger complaint over services no longer even asking for a number.