If you're truly salary, then you don't have to work 40 hours a week. I'm called salary, but that refers more that I'm not part time. I have to work 40 hours a week, seat in chair hours, and they make that very clear. Again, if I work more than that, they have to compensate me somehow, so I'm not really what normal people call salary.
I would count some of the time you're working at home. My last job had a rule, if you get called at home for work, you charge at least 2 hours. You're probably multitasking while you send those texts, so if you want to be generous, you could count half of that time. Realize, people like me work 40 and never get calls outside that 40. That work you do outside normal hours is valuable and comes at a cost to you.