Owners of its latest generation iPhone must get a proper grip on the handset, Apple has said.
As analysts on Friday fired off predictions that opening day iPhone 4 sales would easily top a million, Apple dismissed complaints that cupping the smartphones in a way that covered the lower left corner cut signal strength.
"All phones have sensitive areas," Apple chief executive Steve Jobs was quoted as telling technology-focused Ars Technica website in an email. "Just avoid holding it in this way."
Aspiring iPhone 4 owners swarmed Apple stores in Europe, Japan, and the United States on Thursday in a launch that rivaled the release of the first iPhone by the culture-changing California firm.
Some new iPhone 4 owners discovered that holding their new smartphones so that their palms covered the lower left corners choked off the strength of the telecom service signals.
Apple designed silver edging on handsets to be part of the antenna system to improve signal strength.
The problem could be fixed by moving one's hand or encasing iPhones in rubber "bumper" frames that Apple sells for 30 dollars.
"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," Apple said in a statement on Friday.
"This is a fact of life for every wireless phone."
Apple advised those that experience the signal problem to "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."
Antenna concerns did not appear to deter the hordes that descended on Apple stores on Thursday. Oppenheimer analysts Yair Reiner and Michael Suh raised their estimate of iPhone 4 sales to 1.5 million.
"Guessing first-day iPhone sales is somewhat meaningless but hard to avoid," the analysts said in a note assessing the iPhone 4 marketplace debut.
A sample survey of iPhone 4 buyers indicated that only 26 percent of them were buying the smartphones because an old phone was failing and that 76 percent owned a previous generation of the gadget, according to Oppenheimer.
"I've been an Apple head since I was a teenager," said Richard Polote, among those queuing to buy an iPhone 4 in San Francisco on Thursday.
"I feel pretty confident that whatever problems do arise, Apple will solve them in a timely fashion with upgrades or whatever," Polote said.
Features luring people to the iPhone 4 include high-definition screens and "FaceTime," which uses a forward facing camera to enable video chat.
"I think these issues will sort themselves out," said Gartner technology analyst Van Baker. "It is a very impressive phone."
The original iPhone launched in 2007 brought smartphones to the masses. Apple has sold more than 50 million of the handsets in the past three years.
But its latest version enters a crowded market full of rivals boasting bigger screens and running on Google's open-source Android operating system, which is more accessible to developers than Apple's tightly guarded system.
Sales of a white iPhone 4 model have been delayed to the second half of July because of unspecified manufacturing difficulties.
Carriers in the United States and France were forced to suspend early orders because of heavy demand. Apple said last week that it set a single-day record of 600,000 orders for the new smartphone.
The new iPhone will be available in 18 other countries in July and 24 more in August.