Thanks Mark. Good idea. Would the group be accessible from all devices (and not just phones)?
Whatever I go for, there is going to be somebody who doesn't like X and somebody that doesn't like Y. No offence to those that like X.... or Y for that matter :)
So, the options so far are WhatsApp and Facebook.
I'm going to vote Facebook. It takes seconds to create a Facebook account and it is accessible from all devices.
Any other votes?