American Technology Research analyst Shaw Wu on Wednesday joined a chorus of other analysts in forecasting Apple to introduce a new version of its iPhone handset around June.

“Our checks with supply chain sources indicate that the iPhone is likely to undergo a product transition in the June-July timeframe, about a quarter earlier than expected,” he wrote in a research note to clients. “We had previously thought a 3G version would be available in mid- to second-half . Besides a software upgrade to version 2.0 in late June, we now believe we will likely see new hardware as well.”

Giving the analyst higher conviction is the accelerated timetable in which iPhone inventory levels have gone lean, which he said is consistent with Apple’s tendency to wind down stockpiles ahead of an update.

“We believe Steve Jobs could unveil these new iPhones at his WWDC keynote in early June,” he told clients. “In addition to a 3G version, our sources indicate that the 2.5G model could see a minor casing change and lower price point closer to $299-349 vs. its $399 price today.”

While the iPhone currently stands as a relatively minor contributor to Apple’s top line, generating only 2-3 percent of the company’s revenue, Wu believes it will one day become as large as the current Mac business, fueling approximately $15 - $20 billion in annualized revenue.