Interesting. I am wondering if there is a way to figure out WHO ALL out of my Phone book have iMessage / iPhone?
Then I'd message them on iMessage instead of WhatsApp or SMS (Preference order: iMessage > WhatsApp (I can see who all are on my whatsapp) > SMS)
Initiate a text message via the Messages app and enter the recipient's phone number. If the number turns 'blue' then that person has an iOS device with iMessages enabled. However, if the number remains green, the text message will be sent via SMS.