It's been THE news of the week for the wireless industry that Verizon has selected to go for LTE as their next generation network rather than UMB, the successor technology of their current CDMA1x EvDO network. I put down my initial thoughts on the deal here. In the meantime there are two additional important points which came to my mind: Multimode terminals and backwards compatibility!
UMTS operators that are upgrading to LTE will have a smooth migration path especially since mobile devices are likely to be GSM/UMTS/HSDPA/LTE compatible. LTE makes this especially easy since the air interface has been designed to be able reuse oscillators etc. from HSDPA. Also the software stack on higher layers will probably be partly reusable as I expect that high level (NAS) signaling will be similar.
CDMA operators such as Verizon will have a much more difficult story to tell their subscribers. I kind of doubt that there will be CDMA/LTE mobile devices since there won't be many operators taking this path. Also from the core network point of view LTE won't be able to interconnect with a CDMA network as easily as with a UMTS network. For UMTS, the LTE specification already contains all information of how to do handovers back and forth between the two worlds.
A small comfort for Verizon: Sprint will have a similar experience moving from CDMA to WiMAX...