That is incorrect also. T-Mobile uses UMTS Band IV (1700) in many locations. The telephone you mentioned uses UMTS Band I (2100). UMTS Band I (2100) is not used anywhere in the United States because of interference from UMTS Band II (1900).
And even then, it may not have the right bands for AT&T. When they make these global phones, they are intended for overseas use. Take the HTC Droid Incredible 4G LTE. It supports GSM. It has quadband support for GSM/EDGE, but only 900 and 2100 mhz radios for UMTS/HDSPA. So it will only get voice and 2G. It may get some 3g on t-mobile.... but only in the areas using 2100.
So be sure to take that into consideration when you look at buying a Verizon global phone.