You don?t need cell service to use your phone as your primary GPS. As JimP said, get the OnX app for $30 (less when it?s on sale) and download the maps of your area via the app at home. I bought a GPS (64s maybe) a few years ago for a future WY lope hunt and used it this fall and paid $100 for the OnX chip to use with it. I ended up going solo so a family member gave me an inReach for some peace of mind for all of us. Along with my phone and the OnX app, that gave me three GPS options.
Based on my experience, I would use my smart phone with OnX, take a good portable charger, and a Garmin inReach. The inReach would be excessive for a lope hunt with buddies. However, the wife liked the inReach because she knew I was OK, my Dad who couldn?t go due to disability liked it because he could follow along on my hunt from WI, and I liked it because if it hit the fan I could get help. I used my phone almost the entire time to navigate due to better detail and resolution vs the 64s.
You can definitely do a lope hunt with just the OnX app for your phone and a portable charger (which u probably already have or could borrow). Save the money on the GPS for now and decide after your lope hunt if you want one for your deer hunt.