Your reminder messages should be less than 140 characters. If your message needs to be longer, then you can enter up to 320 characters. If your message is more than 160 characters, then it will be broken up into 2 separate text messages on some phones and carriers. Keeping your reminders under 140 characters allows some room in case your customers have long names, or there are any other template tags that you're inserting into your reminders.