Cells phones are extremely useful for a lot of things. They take great pictures. You can also use the phone's GPS to help find the correct approach and exit. There are some great apps for canyoneering beta and also navigation. But you should always have a backup plan for when the cell phone breaks or the battery dies because inevitably it does. Canyons are also extremely rough on phones. Even if you keep it in a dry bag or protective case, it could get damaged. I destroyed one phone when my dry case opened and filled with water. If you need the beta or maps, you should carry a paper copy as a backup.