When the 3G came out , it took me until october to get it. 3GS , about 2 hours on launch day at the 5th Ave Apple store.
The i4 will probably be just as hard to get as the 3G. Of course apple did in fact speed up the amount of time customers spent on line if they were upgrading, however, Your best is to wait until the following week or maybe even the following TWO weeks so that all the nerds can get their hands on it first.
That way you wont be in line for ever or be turned away because they ran out of stock. You can still try though since you're not in a big city like NYC.