Activating over the Internet has always worked for me, even when re-installing (after a few months they "reset" the information so the system doesn't disallow Internet activation again). Of course you need a network card that Windows has a driver built in for, in order to do the activation during installation. If it can't load a driver, you just tell it that you'll activate later, finish installing, and after you get the network card working do the activation.
Only once I think when installing a friend's system did I have to activate over the phone, and it was quick and painless, though it takes a while to read the numbers off and then get the numbers you need.