Wish I can just enter a phone number within Whatsapp and start texting

I have a lot of people that I need to communicate with via Whatsapp, but only for short conversations (with only a few back and forth). Then the contacts are no longer needed.

It is quite troublesome to have to go into address book, add the phone number as a contact, wait for the little Whatsapp contact to show up, and finally I can start texting. After I am done with this person, I have to go back to the address book and delete the contact.

I hope Whatsapp can simply let us entering the phone number right within Whatsapp without adding as a contact, or can this be done already?