On an iphone, when you send a text message, apple will take a look at the phone number you're sending it to and check if it's linked to an imessage account. If

On an iphone, when you send a text message, apple will take a look at the phone number you're sending it to and check if it's linked to an imessage account. If it's linked to an imessage account, you're not sending a text anymore, you're using an internet service just like whatsapp. There is no technical relationship between SMS and imessage, but to the user it's the same interface