The iPhone 5 is going to be revealed today. We can also expect the device to actually launch later this month on September 21. There are other phones on the market, like Samsung's Galaxy S III, that might challenge the iPhone 5, but Windows Phone 8 isn't going to be one of them.
A report out of The Verge indicates that Microsoft isn't finished with the core software in Windows Phone 8. They put on a strong showing, even with faked ads, at a joint press event with Nokia. Other manufacturers, like Samsung, are also beginning to show off their Windows 8 handsets. It seems that the only company who's not ready for the launch of Windows Phone 8 is Microsoft.
Windows Phone 8 was expected to launch in early October. This would have put it ahead of the launch of Windows 8 and would have given Microsoft enough breathing room to effectively market both. That launch date is now gone and replaced with a tentative October 29 launch, only three days after the launch of Windows 8.
The main culprit behind the delay is testing on the part of handset manufacturers and carriers. The Verge says that HTC seems to be the manufacturer having the most trouble with Windows 8, but carrier testing may push the launch back even further as they wait for HTC to get it together.
A delay into late October/early November could really hurt Microsoft's momentum in going forward with Windows Phone 8. They advertise it as the next best thing, but the iPhone 5 will have been on the market for a month before Microsoft is able to push out their Windows 8 handset. Any momentum they may have gained by showing off the Lumia 920 before the iPhone 5 reveal has just been killed.
I still believe in a future where Windows Phone 8 will meet with some success, but Microsoft is getting off to a rocky start. They're going to have to really push Windows Phone 8 this holiday season if they want to have a decent end of year showing.