Depends on the coverage in the area and the network. If ideal coverage etc it should work fine.
Usage could be very high, i.e both ways 720p video would chew through 2gb in about 20mins, if the connection supported it running at full, but thats the extreme end of the scale and makes a few assumptions about the speed of the connection available etc.
Skype automatically adjusts it's codec settings based upon the bandwidth, so it's hard to set it at "maximum quality". Typically speaking however you'll use a minimum of 1Mbps in both directions for a 720p video call, more if the bandwidth is available.