You can turn on your phone in airplane mode of course (to watch a movie or use an e-reader or listen to music).
Here is the list of airlines that you CAN officially use a GPSr on:
http://gpsinformation.net/airgps/airgps.htm. There's actually quite a few (including Delta and United). I think in most cases, you still need to ask though, to be on the safe side so an air marshall doesn't tackle you and the plane gets diverted and they haul you off and you get "interviewed" for two days.
I believe in all cases (or most), these have to be standalone units (which only receive, hence the "r" in "GPSr", whereas your phone might actually transmit the location for an app, which would be a big no-no, not to mention Google maps would be trying to download maps...)
I used my Garmin 60CSx on a flight about a year ago with few problems, and it was interesting to see the elevation/speed, etc.
If you are lucky enough to be on a flight with wireless (and feel like paying the fee), you can use something like the flightstats website. I'm not sure how "real-time" it is, but it overlays the flight on top of a google-maps. You can check it out below by just clicking on "track random flight":
Flightstats Web Site
You can change the overlay to "hybrid" which will give you a satellite view and streets. Again, I'm not sure how real-time it is (it could be a few minutes delayed), but it's something.
I suppose if the flight has wireless, you could connect your phone to it and use the GPS in the phone and google maps, but again, that's getting into borderline issues with flights and cell phone usage (who knows what a flight attendant might see and assume you're doing with your phone). The one time I used my GPS, I made sure to ask the flight attendant so she'd be aware what it was I was holding and doing. But there's no guarantee that your flight attendant will know if GPSr's are allowed or not (even if the particular airline's policy allows them). If she/he is not, I wouldn't push the issue.