It was hacking because AT&T certainly didn't intend for people to be retrieving other people's personal information by randomly guessing ICCID numbers, and changing their User-agent header.
Look, I'm not arguing that this should be criminal behavior, and it certainly doesn't merit a jail term. I can't tell you how many times I've done stuff exactly like this - probably in the hundreds of times. Is it hacking when I paid $15 for a 1 week pass and then used curl to download 11 gigabytes and 10+ years of the American Journnal of Clinical Nutrition? Probably. But, to give all due credit to the AJCN, they detected my repeated queries, and redirected me to a page that asked me to wait 30 seconds between each query when doing bulk downloads.
So, there is a case where I wasn't doing the obvious (downloading through the web interface), "hacking", if you will, but the AJCN was clearly fine with it, they just wanted me to ease up a bit, and instructed me how to do so in a friendly way.
If weev is guilty of anything, it was not realizing that posting high-profile individuals names onto gawker was probably a Really Bad Idea (TM).