Technically its not easy to fix the antenna problems with a software unless the iPhones are using some sort of smart antenna technology which uses software to "tunes" the signal strength (which I don't think Apple is using) coz they have boasted about the new Antenna body design.
Hardware method is the easiest way and that's why they introduced the iPhone 4 case "bumper". Technically its called "RF absorber". Many designs have used this method to reduce the RF interference. However, I am not sure other "plastic case" design by other manufacturers have same quality as Apple Bumpers or not.
However, I believed the software patch (as mentioned by Apple Insider) 4.0.1 (if released) is not trying to solve the Antenna problem but instead the software patch is trying to close any security holes for Jailbreak solutions. :hehe: