You can send free text messages from the cellular providers websites. I have U.S. Cellular so I go to their site and send reminders to my DH through the day. This works great when I don't have time to talk, or if I know he isn't available to take calls.

This also works when you have friends/family whose cell numbers are long distance for you. This way you can leave a message, get your point across and if they want they can return your call, and you don't have to place a long distance call.