Since you've written this in the "iOS and Apps" section, I have to assume that what you're really asking is "can I email or text a message to a group ON THE IPHONE, IPAD OR IPOD TOUCH"?
Assuming this is correct, the answer to the question is yes, BUT.
The "yes BUT" is that you can only email or text groups that have been pre-defined in your Contacts list/Address Book. Which you do on your computer.
So, for example I would fire up Address Book on my Mac, create a group called "Family," move the appropriate names there, then sync my iDevice. Now, if I want to send a text or email to everyone in that group, all I have to do is press the + button, add the group, and press send.