How do you manage lead phone numbers of various type like mobile, work, home using only one input field? 

It looks like a lead has only one work phone number. 

Where do you keep the information about other phone number? 

What happen with a lead having a mobile phone number during "deal conversion"? It looks like it will become a work phone number. Then you loose the information about the phone number type (mobile) and the opportunity to know that you can SMS the person to follow up.