Corrrection: Verizon has publicly stated that their LTE rollout will not be complete until around 2013-2014. So, as they begin to rollout LTE phones (next year), they need to ensure that they can fallback on CDMA for many years to come. Verizon needs to rush their LTE network now in order to attract the latest phones.
AT&T has the "luxury" to enhance their 3G network to faster speeds (7.2 mbs now, next is 14.4 mbs). Verizon's CDMA is, for all practical purposes, dead as far as ability to enhance. CDMA is stuck at 3.1mbs (yes, I know....all these speeds are theorteical). AT&T is tesintg LTE now, and will rollout next year as LTE phones become available. I'm not a cell engineer, but I heard that the LTE standard is still not final. I hope that all this equipment that they are deploying (Verizon and ATT) is field upgradeable via software updates.
Sprint is kind of going in their own separate way with their 4G Clearmax solution. Yes, they were first to build a 4G network but this might hurt them in the long run as they try to attract the latest/greatest phones. Will Apple ever produce a Clearwire iPhone? Doubt it.