Can't say for Antarctica, but on the Silversea Explorer in the Arctic (2009) the internet was extremely spotty - we didn't sign up for a package because it was quite pricey, (charged by the minute,) but Ngaire did. She noticed that when CNN or another channel came in on the TV then the internet did too and she would quickly send out a pre-composed email. They have a couple of computers in the ship's library - I don't imagine the reception is any better there than in your cabin, but not sure. Maybe the group who went in 2010 can fill you in on that.