Ethnio allows you to automatically remind your participants of study times via email, text message or phone call. You can set these up in Scheduling >> Reminders.
You might be wondering why you can't send emails or text messages from your own email address or phone number. Security, in a word. For now, you can change the from "name" but the email will be firstname.lastname@example.org. Sorry - we know this isn't ideal but it turns out sending email from you is rather dicey.