Hangouts 4.0 how do you switch between SMS and hangouts on one contact

I like using hangouts for my T-Mobile SMS.
I go the new hangout 4.0 today. I can't figure out how to pick which method a message is sent to a contact that has both SMS and Hangouts in their contact info. It seems like you must message them based on what ever the last incoming message was.. either SMS or hangouts..

Anyone?