I've just tried on my iPhone to print to an Epson SX515W which is wirelessly joined to my network with 10.6.5 10H568 (an older build) and it doesn't work.
I haven't tried plugging it into my computer and going from there yet as I'm to tired to try but if people do, I will give it a go
The wireless printer must support airprint. If you are using your mac to connect to your printer to print normally, you have to share from your mac.
Just because your printer is on a wifi network doesn't automatically mean it's airprint compatible.
You have to share your printer over your wifi network from your mac if it's a non-airprint compatible printer.