HTC has dropped the kernel source files for the HTC First, an AT&T exclusive we reviewed back in May. These source materials will allow the First's [few] developers to provide better support for the device, and make custom kernels a possibility. Of course, this all depends on the development community, and I'm not sure just how much of a following the First has in that regard.
Two kernel source versions are available, for builds 1.08.502.1 and 1.05.502.1. Both can be found on the HTCDev site at the links below.