Design experts have criticised the phone design, saying it exposes the antenna to touch. While this problem can occur in all mobile phones, the design of the iPhone 4 makes it more susceptible than others.

Analysts say Apple has created a public-relations headache for itself by appearing to dismiss or ignore the problem, allowing a minor issue to be turned into headline news.

Recall unlikely

Although most analysts believe a recall of the device is unlikely, a growing chorus has urged Apple to resolve the matter, perhaps by offering free iPhone cases, which appear to solve the problem.

The iPhone 4 has been an unqualified hit with consumers, and sales have so far been unaffected by the controversy, analysts say. Apple sold 1.7 million units in its first three days to become the fastest selling device in the company's history.

But scattered reports cropped up early on from users who complained about decreased signal strength when they touched the antenna. The company has been sued by several consumers over the matter. Still, the problem does not appear to be widespread.

Earlier this month, Apple issued a statement, saying the problem was caused by a software glitch that overstates network signal strength. But some found that explanation wanting.

Many who follow the company believe the problem is with the hardware itself.

The influential publication Consumer Reports said on Monday it could not recommend the iPhone 4 to buyers because of problems with its signal-strength.

It has called on Apple to provide a free fix to iPhone 4 buyers. Shares of Apple closed up 0.4 per cent at $252.73 on Nasdaq on Wednesday.