The BeerAlchemy Touch iPhone app doesn't get as much credit as it should. It is essentially the exactly the same application as the Mac version, except that it is only $4.99 as opposed to $29.95 for the desktop version. I've been playing with it for weeks on my iphone and haven't bothered to pay for the desktop version yet. I can't find anything in the desktop trial that the "touch" version doesn't also do, with essentially the same UI.
But to the original question, you can sync between the desktop and iphone versions as long as you're on the same network. It's simple and keeps everything in sync between the two, but I'd just jump in and buy BeerAlchemy touch if I were you. There's a lot of stuff I wish it did, but even still, it's the best $5 app I've gotten to date.