The newly issue/ bug found in the iPhone 4 which is Losing Signal while Holding iPhone 4 has been Discovered yestarday and was discovered in the iPhone 3GS by 2008. So Jobs decided to reply on of his iPhone 4 owners about this issue telling them to Avoid holding it in that way!
Also, he replied C.K. of SampletheWeb, The official Response was
Gripping any mobile phone will result in some attenuation of its antenna performance, with certain places being worse than others depending on the placement of the antennas. This is a fact of life for every wireless phone. If you ever experience this on your iPhone 4, avoid gripping it in the lower left corner in a way that covers both sides of the black strip in the metal band, or simply use one of many available cases.