Powerpage.org cites a Wall Street Journal article reporting that Apple has worked with AT&T to "rejigger" how the iPhone works with AT&T's towers, resulting in a reduced load for some tasks. It was not clear what changes were made, but apparently a "crash course in wireless technology" allowed them to figure out how the iPhone can get along better with AT&T.
Such news indicates the lengths that Apple is willing to go to in order to be a good partner with AT&T. While few people are singing AT&T's praises, apparently there is an effort within the company to improve the network in large cities to reduce the number of dropped calls. According to Powerpage, "A random performance test released in February found that AT&T's 3G network speeds had improved by 84%."
The problem is that AT&T's 3G speed has never been the main issue. AT&T is, and has been, very happy to compare themselves to Verizon when it comes to 3G speed. When it comes to reliability (i.e. how well you can actually use that speed) and availability, however, AT&T's 3G has consistently come up short.
Not to mention that whole tethering issue that AT&T hasn't mentioned in several months, despite having originally promised it would be available by the end of 2009.
If Apple is working on a CDMA/Verizon-compatible iPhone, AT&T's efforts are probably going to be too little, too late. After almost three years of consistently disappointing iPhone users with poor 3G availability, dropped calls, late availability of MMS, and even later availability of tethering (assuming it is ever available), iPhone owners have little reason to stay with the company.