Let the hive mind of Engadget get that for you.
"I own an iPhone 3G and I'm looking for a decent speaker / alarm clock for it. I am going to listen music in a mid-sized room, so I want nice quality speakers with solid bass. I also want to use it as an alarm clock, so it would be great if there is such a feature. The price can be low-mid to mid-high range. I was looking at the Klipsch iGroove SXT; it's powerful, slick and the reviews are good, but it doesn't have an alarm clock feature. It's no deal breaker if I can set it up from the iPhone, but I'm not sure. Thanks!"
Yeah but I can imagine with multitasking OS, its just like with Windows, where if you're working on Photoshop and someone phones you on Skype, even if the program is minimised and not "open" it would be able to leap to the front and alert you. Its a real shame something like that isn't possible on the iPhone at all.
I haven't really fully understood *how* push works, but the way I've broadly gathered, I don't think it would be possible to have a VOIP call be received via Push.