The Windows Phone version of Halo: Spartan Assault will come to the US exclusively via Verizon – at least initially. Verizon makes no mention of how long its exclusivity will last, noting only that Verizon customers will get the Halo spin-off "first." The game will be sold for $6.99 and will be compatible with all four of Verizon's Windows Phone 8 models.
If you don't have a Windows Phone (or a Verizon contract), Halo: Spartan Assault is also headed to Windows 8 PCs and tablets. The game is slated to arrive this month.