Solved! See bottom of post for an update!
It seems that my Google Voice number (262) 204-7265 is no longer accessible from my Google Apps account: [email protected]
I originally set up my Google Voice number to be associated with my Google Apps account. I had recently deleted that email address in order to turn it into an alias of Continue reading Help! My Google Voice Number Still Works, But Is No Longer Associated With My Google Apps Email Address.