I'm unaware of any "go to date" function on the stock calendar. There are two workarounds. Both of which are kludgy. You can display by list and scroll to contacts past or future, but if you have no contact on the day you want that won't work, and if you have loads of appointments that may not work too well. Second, you could make a new entry, then scroll to a date in the future at least, and when you're done with the contact you're on the date. Frankly the default calendar is not very good. The stock palm calendar was much better. That said I used a third party calendar on the palm and I do the same with the iPhone. I use Calengoo, which does have a jump to date function on its default screen.
Unfortunately, no calendar program on the iPhone is as good as datebk was on the palm.