Without reading more than the OP and thread title, I have a feeling it's one of those cases where the fact that a person spends 4 hours a day doing nothing but talk on the phone (meaning they might be much more likely to be the type that won't excercise or just in generally poorer health?) has more to do with it than the actual usage of the cell phone.
If you replaced the phone with a banana (so they held it up to their ear for 4 hours every day and did whatever they usually do) you might get the same effect. Who knows.