Apple's next iPhone won't be until late 2016, but should come with a new design.
iPhone 4 Signal Strength Indicator Issue Alleviated by Use of Bumper or Case
In his iPhone 4 review for The Wall Street Journal, Walt Mossberg did note the device's tendency to show a lower number of signal strength bars than the iPhone 3GS, but that calls did continue to go through and Apple reported that the issue is simply a software issue with the display of the bars rather than an actual signal strength issue.
The cupping issue, however, may be more significant than just a software presentation issue, as several users have reported dropping calls as they place their hand over the lower left portion of the phone.
One user has posted a YouTube video demonstrating the issue and the use of a slide-on iPhone 3GS case to eliminate it.
We have confirmed that Apple's bumper case also appears to effectively prevent the issue from occurring. It remains to be seen, however, what Apple's official response to the issue will be.