Verizon Wireless is known for being the largest CDMA network here in the U.S., and for that matter, the largest carrier in the U.S. period. They also operate CDMA networks in Canada and Mexico and some other countries, however, reports state that Verizon will be shutting down their CDMA networks in these areas and switching to the use of GSM and LTE networks strictly. Verizon's decision to make the jump to GSM in these particular areas is in regards to the improvement of their roaming efforts in those countries where GSM/LTE will be adopted, which will allow them to also expand upon the roaming in Mexico, thus allowing their customers more capability to roam when traveling in that country.
What this means for customers here in the states is that when traveling in Canada where Verizon will be shutting down the CDMA network services, for a time, they'll only be able to roam using 2G data. That will end up taking effect sometime next month according to the internal Verizon memo which lists the details of the changes to the networks. It also means that those who wish to roam in those areas where GSM and LTE will be adopted, will not be able to roam via CDMA after the services have been shut down so those who don't have a device which supports GSDM/LTE roaming will likely need to update their device or roaming won't be available.
The memo doesn't state how long it will be until the networks are retired, but with global carriers making the switch to GSM/LTE, Verizon is in a way being forced to do the same so they're customers will continue being able to roam. This change will also open up roaming capabilities in 220 countries where it wasn't previously available which also means 4G LTE roaming will be a benefit when available. While the memo clearly states this is a change coming to the CDMA networks in global areas, it begs the question if Verizon will ever employ the same tactics here in the U.S. where their CDMA network is still very much in play.