Hey Blown, good point. When playing games, yes, it could be a bit of a problem, but I hardly find any issues with that personally. However, I'm holding it with my fingers on the back of the phone not on the edge where the speaker and mic are. Yeah I know, another "not holding it right" type of...
I'd personally go for the iPhone. Considering Apple being very strict app-wise -- in terms of quality, with 99% of the apps I've used I haven't had any problems. Skype included.
For your exact dilemma, I'd suggest checking out some in-depth comparison like Samsung Captivate vs iPhone 4...