My Verizon cell phone works reliably from cruising altitude, but my previous Sprint phone did not. (NB: non-passenger airplane!)
Does it work over the ocean? I don’t think so... when you’re cruising at altitude over land, you are only 7 miles in the air. Add in a little horizontal distance, and you might still be no more than 10 or 12 miles from the tower. In the middle of the ocean... you’re hundreds of miles from any tower—you can’t connect.
If you don’t believe me, try to use a US cellphone on a cruise boat. It stops working an hour or two out of port (not counting using the outrageously expensive on-ship link).