Video calling works on Wi-Fi, 4G, and 3G, but you might want to stick to Skype voice calls if 3G is your only option. Video calls on 3G are very low quality and it's very hard to actually see who you're talking to. If you've on Wi-Fi or Verizon's LTE network, the audio andvideo quality is pretty decent and looks just as good as what you would get on a netbook with a built-in webcam.
Since the Skype Video all is built specifically for the HTC Thunderbolt mobile phone gadget, don't even both trying to install it on another phone. We whipped out a half dozen devices and the only once it would successfully install on was the Thunderbolt. Hopefully Skype is already working to add compatibility with other HTC handsets since the majority of the new devices have all launched with a decent front-facing camera.
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