Unfortunately, it's not possible to add SMS reminders directly through DigiCal. There's however a workaround of it using the web interface of Google Calendar (www.google.com/calendar).
You can set up a default SMS reminder for one specific calendar in the web interface of Google Calendar. So for example if you have a calendar called "Work" and you set up a default SMS reminder for 30 minutes, then you will get for every appointment in the "Work" calendar a sms 30 minutes before it happens.
Event with SMS reminders are shown in DigiCal's event dialogue.
Customize your notifications
Google Calendar offers different options for receiving event reminders. You can choose to receive your event reminders via SMS messages, emails, or popups within Google Calendar itself.
Here's how you can customize your reminder settings:1. In the calendar list on the left, click the down-arrow button next to the appropriate calendar, then select Reminders and notifications.
2. In the Event reminders section, select the reminder method from the drop-down menu and enter the corresponding reminder time (between five minutes and four weeks). If you'd like to add additional default reminders, simply click Add a reminder.
3. You can also choose to be notified of specific activities on the calendar by selecting the appropriate options in the Choose how you would like to be notified section.