On the iPhone how do you make it so your text says imesage?

Like when you receive a message and it says "imessage" instead of the actually message?

Whenever I text someone and iMessage doesn't kick in, I normally just send a few texts then suddenly it'll go randomly. The only things I can think of is text normally for a little bit, see what happens.

Or you can try going to contacts, find the person you want to iMessage and change the phone number from 'Mobile' to 'iPhone.'

Then the last thing I can think of is sending a text then hold it down like your going to copy it, then press 'Send as iMessage.' I don't know if this works like that but I know it does vice versa.

Sorry if none of these helped. :/