AT&T having HSPA upload speed problems in some markets

There's now a rather meaty thread on Mac Rumors' forums detailing problems that iPhone 4 users have had with miserably slow upload speeds in HSPA-equipped AT&T markets -- speeds that had in some cases been well over 1Mbps before the holiday weekend but have since fallen to 100kbps or lower. A popular theory is that AT&T decided to cap speeds in light of the iPhone 4's success and the danger it poses to network oversaturation, but we're not buying it -- 100kbps is ridiculously slow for an HSUPA-enabled network, even a heavily-used one, and there are huge markets (LA, for example) that seemingly aren't affected. We don't know what's going on, but we've reached out to AT&T for comment and we'll let you know what's up as soon as we do.

Update: AT&T's identified an infrastructure supplier as the culprit and says a fix is in the works.