The FCC recently approved the Nokia RM-877 that is compatible with AT&T's LTE bands, pentaband HSPA+/WCDMA and quad-band GSM/Edge. The FCC documents also not the device has NFC, Bluetooth and dual-band Wi-Fi.
Beyond that, there's not much more to go on but there is a strong possibility that this is the EOS Windows Phone aka 'Elvis' for AT&T. Nokia has requested all the juicy documents that have device photos, schematics, the user manual and device specifications to remain private. So for now, it's pure speculation that the RM-877 and the EOS are one in the same.
There is one schematic was included in the test reports that has the dimensions of the RM-877 being 5.13 inches tall and 2.81" wide. While thickness was not documented (which might have been a dead give away), the height and width is just a smidgen wider than the Lumia 920 which, if the leaked images hold true, is along the lines of what we are expecting the size of the EOS to be.
Could the RM-877 be Nokia's EOS Windows Phone? While there's no mention of a 41MP camera, there is mention in the FCC's public documents of a camera grip. Could a 41MP shooter warrant a camera grip accessory?
While this could go either way. There's just not enough meat on the bone to say for certain this is the EOS Windows Phone. But then again, there's nothing for certain to say it isn't the EOS. The good news is that we shouldn't have long to wait for the July 11th event that should shed a lot of light on things.