Free SMS Alerts for Google Calendar
One of Google Calendar’s killer features is that it can send free SMS message reminders. Unlike many SMS services this works (and works well) in many countries. I beleive that all that UK and Spanish mobile operators are supported. See Google Calendar’s list of supported mobile phone operators
To activate:
1. Click on “Settings” at the top of any Google Calendar page, then select the “Notifications” tab.
2. Select your country from the “Country” pull-down menu.
3. In the “Phone number” field, enter your phone number.
4. Select your carrier from the drop-down menu, if requested. If the “See Help Center for supported providers” message is displayed, leave the field as is.
5. Click on the “Send Verification Code” button and wait for a text message to be sent to your phone.
6. Once you receive this message, enter the code you received in your text message into the “Verification code” box and click on the “Finish setup” button.
via How To Setup SMS Alerts For Google Calendar.