OK, so the current set of scammers are probably just interested in getting money out of the premium phone line. But I assume there's a dialup server on the other end that actually provides internet access, so that people don't notice the scam too quickly.
This means they could also sniff packets to their heart's content, stealing passwords as they go...
The reasons were explained recently by a NASA insider on sci.space.station:
To minimize the number of penetrations through the pressure hull (both the power source and the load are outside, in this case), minimize the number of connections through hatches (lesson learned from Mir), and minimize potential crew exposure to ammonia (used to cool external power components).
Gives a whole new meaning to "lending someone a hand"!
This means they could also sniff packets to their heart's content, stealing passwords as they go...
This is microgravity. You can go anywhere in the station without "setting foot" at all!