Well, it partly works. If Skype is turned on, the iPad rings with an incoming call to a SkypeIn number. Otherwise (or if you miss the call) it goes to voice message. So that's OK.
However it seems that SkypeIn can't receive text messages (SMS). And this then means you can't set up your SkypeIn number for caller ID on outgoing calls, because Skype insists that they send a text message to your caller ID number to verify it. So that's all a bit weird.