That modem – Qualcomm’s MDM6600 – supports both HSPA+ and EVDO Rev.A, though of course both the iPhone 4 and the XOOM only have the latter enabled. It suggests that Motorola may not be swapping out the modem for the GSM versions of the XOOM, the MZ601/MZ603, but simply enabling the HSPA+ support via a firmware change.
Whether that means some bright spark in the hacking community will be able to add GSM support to the Verizon model remains to be seen; it’s not going to be easy, we know that. iFixit also discovered what amounts to a blanking plate saving a space for the XOOM’s 4G modem, implying that will be a new board added in, rather than replacing, the original chip.