Or join the 21st Century and get on Facebook. I would have been notified instantly that way! I have sent you a text but suspect you are already out in the wilds somewhere.
Shame, car is fuelled, clean and sat outside with the roof down ready to go
It's a pretty effective way of getting a message to all your mates in one go that they will pick up instantly (you use it as much or as little as you want to).
A Facebook group would easily work. Set the group up, get people to join, post on the group's page when you're heading out for a blast, others get excited because they have a red dot on their facebook, then decide if they can make it or not. Simple