AT&T has changed its mind about bidding for Yahoo, and is challenging Verizon — and others — in the effort to buy the struggling internet company, Bloomberg reports. There’s no word on how much AT&T has offered for Yahoo’s core internet assets. A second round of bids are due the first week of June. AT&T declined to comment. The telco had been involved in the process through its YP Holdings, which runs the company’s Yellow Pages business — now mostly a digital operation…