A number of users are reporting problems with their iPhone 4.
Apple's latest device went on sale on Wednesday, with hundreds of people queuing outside Apple's flagship store in central London for the launch.
The issue relates to the mobile phone signal, with users reporting a drop in signal strength when the phone is held.
The casing of Apple's latest phone is made of stainless steel, which also serves as its antenna.
Richard Warner, who bought his iPhone 4 on Wednesday morning, 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 'awiginton' 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.
However, it is not yet clear whether the problem affects all phones, or if the signal deteriorates when the phone is making a call or only when held in standby mode.
When Steve Jobs introduced the iPhone 4 at Apple Worldwide Developers Conference, he described the integrated antenna as "really cool engineering".
Apple has yet to make a comment on the current controversy surrounding the latest version of its popular phone.