AT&T’s service is still proving to be an obstacle for new iPhone buyers, according to a small survey conducted by PriceGrabber.com. PriceGrabber, which operates a price-comparison site for online shopping, said it conducted a poll of 2,411 respondents between June 12 and July 10, asking them about why those consumers have chosen to wait to buy the iPhone 3GS . About 10 percent of those polled already owned one of the versions of the iPhone, PriceGrabber reported.