As Illinois law stands right now, there are a number of different laws in different municipalities regarding cell phone use while driving. That is soon to change. On January 1, 2014, Illinois drivers will begin facing fines of $75-$150 for talking on hand-held cell phones while driving. The bill, signed into law by Governor Pat Quinn on Friday, August 1... piggybacks Illinois' existing ban on texting while driving which has been in place for years.
I did a blog post on the topic which you can find here. Texting, or otherwise communicating via text on a digital device, while driving was originally made illegal after a driver killed a downstate cyclist while downloading a ringtone.
Details of the new law and the bill outlawing driving while talking on the phone can be found here.