The memo suggests that customers should avoid covering the lower left hand corner of the phone when they hold it, and reminds staff to tell customers that the phone’s wireless performance is “the best we have ever shipped”. The news is a further blow to Apple’s reputation, which has already been marred by a spate of suicides at the factory in China that produces its products.

The company is already facing lawsuits from at least three customers, relating to antenna problems with its latest model, but Apple’s chief executive, Steve Jobs, insists that owners need to “just hold it right”.