As has been said above the only definitive answer can come from yourself, and I think the most important thing to consider is how you will use the iPhone.
Myself, I love the iPhone, and have used it extensively thanks to my friends that have them, but I am someone who a) does not have the financial means to buy one and then sell it when the 3G comes out and b) will use the iPhone a good deal outside of WiFi range.
Because of those two issues I have been waiting - as patiently as possible! - for the 3G. As someone corrected above, the difference between EDGE and 3G is immense. Not only is EDGE painfully slow (think very early dialup) but when you are mobile and need something on the move and on your feet speed is important.
When I went to the store to buy my iPhone, giving in to EDGE, I turned off WiFi to test the connection speed and it was horrendous. I didn't know whether to laugh or cry, but I did know I needed to put my wallet back in my pocket and leave empty handed.
I suggest trying that... don't open what you have, go to an AT&T or Apple store and test the speed. Turn off WiFi and see what EDGE will (and won't) do.
Understand that the majority of what makes the iPhone unique hinges on its internet connection. If you are someone who will primarily be using their iPhone within range of a usable WiFi and don't want to wait an unknown amount of time (although it is looking more and more like this summer, yay), open it up and enjoy. If you will be doing a lot of on the go use of EDGE/3G I would wait.