Confusing equipment return instructions: UPS or USPS?

Hi. My gateway went out and  AT&T sent me a new one. (three days later than promised, but that's another story) In the box was a sheet with instructions telling me to take the broken one to a UPS store. There was also a label for sending it back via USPS. I don't care one way another as long as I don't get charged for it. Which way should I send it?

Thanks!