I use to speak with my ex in China via Skype but the video and sound was shockingly bad. Often getting cut off or failing to connect altogether. Even if it did connect you could barely hold a conversation. Ok 5500 miles is quite a distance but GoogleTalk is brilliant and get great video and sound talking to her. Plus Skype messages on my iPhone seem to build up unbeknownst to me then about 10 will come through at once. She then thinks I'm ignoring her so I get one or two "how are you?" then "why arent you talking" then "have i done something wrong". It didnt exactly help the relationship (hence ex lol). In my experience Skype is terrible and the new Mac version is atrocious. The UI is simply terrible. I dont use Skype at all anymore because everything about it from what I have experience is just terrible.
If you can use Gtalk its much better in my opinion. You can use AIM app on iphone (and a few others) if you want to use it when mobile.