That the LTE networks operated by Verizon and AT&T are not compatible with each other is something we are already aware of. However, we might be looking at what is the tip of a global LTE fragmentation iceberg, and we seem to be headed in its direction.
According to Wireless Intelligence, LTE networks around the world will use 38 different spectrum frequency combinations by 2015. The number of LTE networks is predicted to reach 200 by that time, or about five times as much there are today. At the same time, the most common 700MHz spectrum, which two thirds of LTE networks globally use today, is what only 16% of them will operate on.
If this unfortunate scenario becomes reality, global LTE roaming will likely be rendered close to impossible. And what hinders it is that manufacturers will have to equip their devices with radios compatible with a huge number of spectrums. Furthermore, switching between carriers will be even more difficult due to LTE incompatibility.
All of that can be avoided if a cross-network LTE standard is established so that all LTE networks use the same spectrum. However, with more and more slices of spectrum expected to be put up for auction and with a multitude of carriers choosing to use a frequency band of their own, that does not seem very likely to happen easily.