The Gear S3 frontier is already available from T-Mobile and AT&T in the United States as both of them are GSM carriers. It's not available via the country's largest mobile carrier because Samsung is yet to release the CDMA variant. Verizon, as many of you would be well aware, is a CDMA carrier. It appears that Big Red may get the Gear S3 frontier soon as a variant intended for it has stopped by the FCC.
Samsung did launch a CDMA version of the Gear S2 (SM-R730V) on Verizon so it won't be surprising at all if it does the same for the current-generation smartwatch. We've spotted an FCC filing for a Gear S3 frontier bearing model number SM-R765V which more or less confirms that the CDMA variant of this smartwatch is in the pipeline for Verizon.
It's unclear at this point in time just how long it's going to take for this Gear S3 frontier variant to be officially announced. Samsung and Verizon haven't said anything about it as yet but FCC filings are normally considered to be an indication that a formal launch isn't that far off.
