Open WAChatz will make your life easier, Now you don't have to save any number to chat on whatsapp. Just enter the phone number by selecting country code and it will open that number in whatsApp chat (if the number is registered on whatsApp). You can also save the entered numbers with name (optional) by enabling "save for later" option. You can also put a pre-filled message, which you can send when you click on "Open Whatsapp"