In short: There's an expectation the first round of 5G phones that become available will arrive as carrier-exclusives. This is likely to be the case not because these phones are necessarily exclusive to the carrier in the traditional sense, but more a result of the phones only being primarily compatible with the exclusive carrier's network. The information on this has come from a new PCMag report, which credits comments attributed to AT&T's VP of Radio Networks and Device Design, Gordon Mansfield at Mobile World Congress Americas.
Background: The problem here seems to stem from the difference in approaches each carrier has made to its 5G deployment. For example, while each of the main carriers in the US seems committed to a 5G rollout, they are all focusing first on different frequency bands. The end result being each carrier's 5G network operates slightly differently on a slightly different frequency. With Mansfield noted further explaining that this is simply an effect of the early adoption of 5G and not something that is intentional from the perspective of the carriers.
Impact: While these comments do highlight the issue surrounding the first deployment of 5G, the impact is expected to be minimal. More to the point, they are expected to be time-limited issues, as in time, and once 5G becomes more commonplace, the issue of different band usage will become less of a concern. A point Mansfield was quick to state, saying the issue is unlikely to "last very long" and "will be very quickly overcome." Therefore, the impact of this is likely to be more dependent on when a particular customer intends to buy a 5G phone. If, for example, the aim is to buy one as soon as possible, then the chances are good that phone will best work with the carrier it's purchased from. For everyone else who waits until the 5G ground is a little sturdier, the option of 5G network support across all the carriers will likely be available. In either case, as AT&T and Verizon have both confirmed on previous occasions (and again by AT&T here), the very first mobile 5G users will have to make do with a puck-like hotspot.