I am not a fan of the way they changed the ability to call the person you currently have messages with. It used to be at the top by their name, now you have to hit the arrow and then call. Its a minor inconvenience but makes no sense why they would add a step to something that wa already simple enough.
I use Google but I did check out the regular app. There should be a drop-down arrow by the name/number. When you click on it the additional features will be there.