Whatsapp, Keeping the number on the new phone but without the old sim card
Whatsapp checks if there's a sim card installed at the time of boot. 
So as long as you have a sim card installed, it shouldn't be a problem to your whatsapp account (The old one)

I've switched sim cards and it hasn't affected my whatsapp account.
The problem of verification arises when you boot your phone without a sim card.