Almost one-in-four potential iPhone buyers in the States have said that they have been putting off their purchase until Apple launches the next-gen 3G model, according to newly revealed market research.

According to the data from ChangeWave Research, a quarter of the people polled in March who plan to buy an iPhone said that they were postponing the purchase until Apple releases a new model (14%) or were waiting for 3G compatibility (11%).

"Assuming Apple's next iPhone is 3G-compatible, it's good news for Apple", a spokesperson from ChangeWave said. "That is the key issue faced by Apple, according to our survey."

And fittingly, ChangeWave's poll revealed that the biggest dislike among existing US iPhone owners was the slow speeds of AT&T's EDGE network.