You place the call from your room. The phone jacks have an extra empty jack you can use for your computer. You need to have a local Orlando number from your ISP you can use. Otherwise you'll have to pay long distance fees. I think some ISPs offer 800 numbers, but they charge extra for that, so you'll end up paying for it somehow.
At all WDW resorts, it cost $.75 to make a phone call, even a local one, so that's where the $.75 charge comes in. It's applied each time you dial in on your computer.
And no, none of the resorts have high speed access. You have to use a plain modem. But the good news is that you probably won't want to do much more than read email. There's so much to do at WDW that it's not like you'll want to play a game online. I guess if someone sends you a big attachment it could be a pain, but we're used to a cable modem at home and don't really mind having to use dial-up at WDW.