Ed and everyone else here broke it down nicely. I would add if you were going to run to the state line or beyond to follow the fish as they move out with warming temps then marine radio 100%. Sometimes offshore cell service can be spotting. Also takes longer to make a phone call than it does to hop on the radio quickly. In emergency that time will be worth the purchase.
The South End provides useful resources and discussion forums for those that fish The South End of Lake Michigan for Salmon, Steelhead, Perch, and Bass as well as elsewhere in the Region and Chicago area.