Delete their number?

Are you all really that brain dead so you don't remember your loved once phone number so if you delete it - it's gone forever?

And when (if) they call you - you have NO idea whos is this phone number calling?

I'm sorry, who is this?

Yes ?

I don't look at the number I look at the contact

Yep, with the nature of cell/smart phones, it's just not necessary to look at numbers anymore. If you never see the number, it's unlikely you'll memorize it and remember it later.