replace subject & email with tel

hi,
i’m very new to contact form 7 and wp. i’m planning to have a standard contact form in the contact section of my 1 page site, but at the top, in my first panel, I want to have a quick contact form featuring only ‘Name’, ‘Tel’ & ‘Message’ fields. So I’d like to do away with the standard ‘subject’ & ’email’ fileds in favor of a ‘telephone number’ field in this first mini form.

1] Is this a bad idea? I’ve seen videos in which they say that emails with no subject can be rejected.

2] And I wonder if it’s even possible for the contact form to send if the user doesn’t enter an email address?