When I send a text to my brother's iPhone from my iPhone it goes as a text. When I receive a message from him it is an iMessage and my responses go to him as an iMessage. His is the only iPhone to which I cannot send an iMessage. How do I reslove this. His number is listed as an iPhone in my contacts.
I've had this happen before, and it took erasing the phone number and re-adding it to the contact for the iMessage system to correctly "sync up".
Another thing you can try doing is deleting the phone number, and then adding his Apple registered email address first (add the email, save the contact, then add the phone number).