Do you mean the iPhone 4 or the iPhone 5? The iPhone 5 is coming out around the same time as the SG2 in the US. Those two are comparable and are on a similar level in quality. The SGS2 is pretty much better than the iPhone 4 in every way though.
That said, being that you're upgrading from a basic phone, I'm pretty sure you'd be happy with an iPhone 4 or any current smartphone for that matter. The functionality that even the most basic smartphones have over normal phones is pretty substantial. Considering you've gone this long with a normal phone, you're probably not someone who has to have the top of the line, so you could save yourself some money and just get one of the cheaper Android Phones like the Droid Incredible or the Samsung Fascinate (if you're on Verizon). Both are good phones and cheaper than the iPhone 4. If you really like Apple products then you can go for the iPhone 4. Either way, you'll upgrade your phone status big time without killing your pocket.
If you wait for the SGS2 you'll be on the cutting edge since a lot of tests have it performing pretty high when compared to the next wave of smartphones. That said Verizon is charging $300 for the Samsung Charge which isn't special at all, so one can only imagine what they are going to charge for the SGS2.