AT&T Nokia Lumia 920 exclusivity period revealed to be only six months
WMExperts

It worried many people when the Nokia Lumia 920 was first announced as an AT&T exclusive out in the US. New information now reveals that the Windows Phone 8 device will only be tied to the US carrier for a period of six months, after which, it may be released through other US carriers like Verizon or T-Mobile. This means that those who want to get their hands on Nokia's latest flagship smartphone without signing up for a contract with AT&T need only to wait until early Q2 2012 for it to become available as a non-AT&T exclusive.

What Else You Need To Know

  • The Nokia Lumia 920 is one of the world's first smartphones running Windows Phone 8 and is set to be released in the next few weeks.

Other sources

After six months, Nokia can bring the Lumia 920 to any other U.S. carrier it wants including Verizon, Sprint, and T-Mobile. There might be more new Windows Phones on the market at that point, however, including a Microsoft Surface smartphone. - Shawn Ingram, GottaBeMobile  
WMExperts
AT&T Lumia 920 exclusive for six months and some training videos leak too  

AT&T is gearing up to launch the Nokia Lumia 920 very soon—in fact we expect an announcement on pricing and availability sometime on Sunday.

WM Power User
AT&T Nokia Lumia 920 Training videos leak, only exclusive for 6 months  

They were also able to confirm that exclusivity of the handset is only 6 months, suggesting the device may be coming to other carriers like Verizon in Q2 2013.

Other
Nokia Lumia 920 reportedly exclusive to AT&T for six months
PhoneDog
Nokia Lumia 920 rumored to be an AT&T exclusive for six months
BGR
Nokia Lumia 920 will only be an AT&T exclusive for six months
GottaBeMobile
AT&T Has Six Month Exclusivity For Nokia Lumia 920  

AT&T will have exclusive access to the Nokia Lumia 920 for six months.