Since you are asking the question, then yes you should address mobile phones. Each client needs to make the call, your time to design the mobile friendly site costs so you should expect some payment. Sitepoint has some great aricles on how to use stylesheets and images sizes to make a site mobile friendly.
Watched a friend try to read an article on a non mobile friendly site, if it was a business selling something, he would NOT have purcased from them.
When viewing a website on the mobile, its just nicer if the site is made to scroll down on a small screen. Vs viewing the screen type view, trying to go side to side all the time.