distro lists are not an iPhone feature. there is a workaround. what email r u using? i did this on mine. tedious setup, but once done then you can send a mass email to that 'contact'.
Send an email to your contacts (group list) including yourself. When you recieve the email click on the "reply all" choice. Delete the content of the orginal email. You will now see all the contact names in the "send to". I am using outlook 2003 and after I did this I dragged this templet into the drafts file and use it as a templet every time I send out a group email.
cut & paste numerous emails into notepad, then make a new contact with those emails. it's all explained here (How to send group emails from your iPhone — RED66)
there are apps in app store that allow you to create distro lists, however i have not tried any so i can't recommend them.
personally, i don't have to rely on distro lists much on my personal iphone. so i setup 1 or 2 using option 2. seems to work just fine. hope this helps.