Odd, I have 2 Pre3, one is a European one unlocked, and the other is a AT&T unlocked.
There is absolutely no difference between the two, and both simply needed to go to accounts, create a Skype one (or log in) and from there, Skype is available via the chat app, from which I can activate the talk or video mode.
I just retested tonight with both phones and 2 of my Touchpads, aside the very high pitch feedback from the devices being too close to each other, they all worked as they should.
Can verify! - On AT&T Pre3 unlocked Australia.
HP Messaging App-->Dropdown box 'Messaging'-->Preferences & Accounts-->Add IM Account-->Skype.