NEW YORK ( TheStreet) - Nokia ( NOK) has unveiled its first phones running Microsoft's ( MSFT) Windows Phone 8, although the jury's out on whether the Lumia 920 and Lumia 820 can move the needle for the Finnish handset maker. "It's an open question whether the new phones will turbocharge Lumia sales," explained Charlie Wolf, an analyst at Needham & Company, in a note released on Thursday. "With sales of four million units in the June quarter, Lumia has been considered a disappointment." Investors were certainly underwhelmed by Wednesday's announcements, pushing Nokia's stock down almost 16% during the day's trading. In a note released on Thursday, Nomura Equity Research analyst Stuart Jeffrey attributed the slump to a lack of "breakthrough innovations" on the phones and the absence of a tablet announcement from Nokia, which some people had expected. The analyst also highlighted potential risks posed by the forthcoming Microsoft operating system. "Windows Phone 8 still seems at risk of some delays that could result in a weaker-than-expected inventory restocking for Nokia in Q4," he added. Both the 920 and 820 boast a dual-core Qualcomm ( QCOM) processor, and have significantly larger screens than Apple's ( AAPL) phenomenally successful iPhone. The 920 and 820 have, respectively, 4.5-inch and 4.3-inch displays, compared to the 3.5-inch screen on the iPhone 4S. The 920 also offers Nokia's PureView camera technology, a feature which has garnered plenty of post-launch attention. Touted by Nokia as a way to take high-quality photos more traditionally associated with standalone SLR cameras, PureView has already won plaudits for its performance in low-light conditions. It's unclear, though, whether the 920's PureView feature, and a set of advanced location services announced on Wednesday, will be enough to move the needle for Nokia. "On balance we like the new phones and features, but note that at 185 grams the 920 is 34% heavier than its key competitors, and few devices of that weight have ever proven big sales successes," explained Nomura's Jeffrey. "While the software and features look promising, we do wonder if the phone is just too big to be 'cool'." At 160 grams, the 820 is slightly lighter than the 920, although both outweigh the 140-gram iPhone 4S.