Hello,
there is a prepaid data service from T-Mobile available now:
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The stick is from Huawei and got 1700 MHz UMTS and 850 / 900 / 1800 / 1900 MHz GSM / EDGE.
Because of that, the Stick may not (!) be used for AT&T UMTS....
I have not found many informations about validity. Afaik, you only have to use it once a year (witch would be good). 1GB is 50 USD (+tax).