Work just gave me an 8310. It has GPS.
And it’s a frickin’ dog. It’s slow to keep up… whether typing or navigating icons or just trying to close the damn “browser”.
The camera is fixed and you’re gonna be happy on the few occasions when something is not blurry.
If you don’t want to buy the unlimited data plan from your service provider and you find yourself around wifi hotspots a lot, then consider getting the 8320. It trades the GPS radio for wifi hardware. Even without dedicated GPS capability, you’ll find the Google Maps application is able to triangulate your position via cell towers with functional accuracy.
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Oh and the 8310 also has a digital 5x zoom and built-in flash. I expect the same for all of the 83xx.