Many new owners reported that signal strength dropped when the phone was held.
In a statement, Apple said: "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."
Steve Jobs issued his response in a message responding to an e-mail from the Ars Technica news site. Mr Jobs wrote that "All phones have sensitive areas".
The problem is thought to be particularly acute for left-handed owners who naturally touch the phone in the sensitive area.
The casing of Apple's latest phone is made of stainless steel, which also serves as its antenna.
Apple sells a rubber "bumper" that shields the sensitive area as do many other firms.
Richard Warner, one of the first to buy an iPhone 4, contacted BBC News, saying that he thought the phone was "useless in its current state".
"Apple have created a phone that has an antenna on the bottom left-hand side of the phone."
"This means that when you hold it in your left hand, the signal bars slowly fade until there is no signal," he wrote.
A number of videos have been posted on video sharing site YouTube complaining about the reception issue.
One video had an American user running a speed test, with hands on and hands free.
In it, the user 'awington' says that, while holding the phone "it won't even run the test when I am holding the phone... once I let go, it makes a connection and runs the test.
"Hold it a second time, and the upload test will not start."
Social networking site Twitter was full of chatter, with numerous tweets on the reception problems.
The issue might stem from the way the integrated antenna is constructed. One section provides mobile reception, while another is for wi-fi.
Some users have speculated that touching the bottom of the phone bridges this gap, affecting signal strength.
When Steve Jobs introduced the iPhone 4 at Apple Worldwide Developers Conference, he described the integrated antenna as "really cool engineering".
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