I really don't think the adaptor for the headphones is that big of a deal, I don't listen to music "on the go" very much but all it does is add some length to the headphone cord, and I don't even think about the connector. If the length bothers you, Brando sells
this accessory for the i900, a 3.5mm jack adaptor that's only a couple of inches long.
Oh, and the Omnia is amazing. It's my first PPC and so far I'm thrilled with everything I can do with it. It's a good device out of the box, but flash another ROM and it will be leaps and bounds faster.