Global basically everything plus global roaming.
LTE Only is self explanatory. Its 4G LTE or nothing in this mode.
CDMA is not as obvious. This mode is 3G only.
LTE/UMTS/GSM is not as obvious. It basically lets you connect to other US service providers like ATT and TMobile should you provide the Jetpack with an appropriate SIM card.
More info on the relevant cell phone connections: http://www.pcmag.com/article2/0,2817,2407896,00.asp
Verizon Support recommended that I set my 6620L mode to "4G LTE Only". The rationale was that I was in an area with less-than-stellar LTE service and the unit might be switching too frequently between 3G and 4G, causing intermittent "hangs" on the JetPack.
Good advice or ???
> I was in an area with less-than-stellar LTE service...Good advice or ???
The key problem is that you were in an area known for poor service. The experience is most likely going to be poor no matter what you do. There is no harm leaving the device in 4G LTE mode only while in this area. It may not be as fast as you like but you should hopefully minimize disconnections as the device flips to 3G and back.