Update: It's official. Nokia and Microsoft will have two joint press events at Nokia World and in New York on the same day, September 5th. Prominent tech media like GSMArena and The Verge reported that they have received invites designed to look like Windows Phone 8's trademark user interface. In this case, there's no doubt that Nokia will be unveiling its first lineup of WP8 devices.
With Windows Phone 8 slated for a fall release this year, recent reports point at the possibility of Nokia introducing two Lumia Windows Phone 8 handsets on September 5th, coincidentally the first day of its Nokia World event, according to Chinese website WPDang. This is further supported by the reputable Bloomberg, who has mentioned that Nokia plans to announce its Windows Phone 8 handsets "as early as next month at its Nokia World event", citing its source as a "person with knowledge of the matter". This timing is not only crucial and timely, given that the next-gen iPhone is rumored to make an appearance on 12th of September, a week after its Nokia World event.
To add on, Samsung is also said to make an announcement of a new device on the 29th of August, possibly one that runs on Android's recently announced Android 4.1 Jelly Bean platform. On the same page, HTC is alleged to already have a WP8 phone lineup up and going; Huawei has announced that they would be launching a new WP8 device sometime in Q4 this year and Samsung has revealed two WP8 handsets for a Q4 release. Nokia's event is definitely a good time to announce its upcoming gadgets - that is if they have anything to show for, of course.