Having owned an iPhone 3G (not 3GS) and now an iPhone 4, you'll have to pardon me while I recover from my laughing fit.
I strongly disagree with your assessment that "there isn't much differnce with the iphone4 or iphone 3gs."
For starters, the iPhone 4 is:
- Slimmer and more refined
- Much, much sharper text and graphics thanks to the much higher resolution display/screen
- Better battery life
- No signal problems here with my iPhone 4. Are some people having legitimate issues? Sure. Is the phone hobbled or unusable for the bulk of users? No.
- MUCH better at taking photos and the included flash allows me to take photos with the phone that I had to miss taking with my old iPhone 3G.
- FaceTime is wonderful for families like mine and my daughter really benefits from the FaceTime feature when my husband has to travel on business, for example.
And many more.
Feel free to enjoy the phone you have, but I find it absurd to say there's little or no difference between the iPhone 4 and previous generations of iPhone.