Easy enough to determine. Power down the phone, than remove and examine the SIM. If the public part of the word Republic is green, it’s GSM. Otherwise, it’s CDMA.
An ISIM is a SIM. It’s a type of CDMA SIM.
Not terribly important since any type of CDMA SIM may only be obtained from Republic support and they will know which one to send based on phone model.
Bottom line (for good reasons), Republic’s preferred process when activating a new phone is to use a new SIM. Any phone purchased from Republic’s online store will come with an appropriate SIM. All bring your own phones must first be activated on GSM.
Generally, it’s possible to move an active GSM SIM from one phone to another phone. GSM technology was designed with this in mind.
Historically, it hasn’t been possible to move an active CDMA SIM (of any type) between phones. CDMA technology was not designed to accommodate doing so, though there have been attempts (with varying degrees of success) to make CDMA SIMs behave more like GSM SIMs for this purpose. Further, it is not currently possible to move an active CDMA SIM (of any type) between Republic phones. Such a swap (if it worked at all) would first require activating the target Republic phone on GSM. After doing so, one might attempt reactivating a CDMA SIM in the new phone. If it works (in my estimation at best a 50-50 shot) great. If not, one will need to request a new CDMA SIM from support. Again, based on phone model, they would know which CDMA SIM to send.