The same Hologram SIM you use to access one operator or radio access technology (RAT) can be used to access any other operator or RAT that we support. This includes narrower-band RATs like Cat-M1 and Cat-NB1 without the need for a separate SIM, as well as 2G, 3G, and 4G/LTE.
I’m going to go deeply technical here to add as much context as possible (to help any possible additional audience of this post, as well as those who have already commented).
Note that the Cat-NB1 specification does leave a lot of room for possible variance between operators as well as requiring only a subset of traditional mobility features, i.e. tower handoff, so Cat-NB1 developments are still emerging. I’d expect this to be a little different from operator to operator on a global scale, while Cat-M1 is quite consistent, similar to wider-band and traditional RATs.
As for operator selection, multi-band/multi-RAT cellular modules implement a scanning routine that scans for available operators and (so long as permitted by the SIM) will attempt to connect to operators’ towers on channels whose RSSI and quality are above thresholds set within the module’s baseband/radio chip. The Hologram SIM will enable access to all operators we currently support, so it’s up to the specific module to determine which tower is a candidate meeting necessary criteria for connecting. The Hologram SIM and the Hologram network both do NOT perform signalling-based operator steering (a practice that became common among some consumer MVNOs, but can be disruptive to the operator selection routine on cellular modules); so, it is literally true that the cellular module in the device performs operator selection internally and will attach to the tower(s) it deems good candidates, which it is designed to do, and is a best practice.
In general, automatic operator selection (set via AT+COPS=0 if issuing AT commands directly) and automatic RAT selection works very well on the majority of multi-band/multi-RAT cellular modules on the market—module scanning times can vary, but the most variance will occur only during initial (cold-start) connections, whereas subsequent (warm-start) reconnections usually occur within seconds of module boot if unimpeded. In the general case, it’s best for host/application processor (UE) firmware to avoid impeding automatic operator selection and, especially, to not prematurely reset the module during its network scanning routine (i.e. firmware that favors event-driven programming and that responds to events/errors/URCs tends to work better in the field than firmware that strictly utilizes timer-based timeouts or watchdogs, and this is true for all SIMs and not just Hologram’s SIMs/network).
There are some cases where manual network and/or RAT configuration can make sense, but it largely depends upon the specific cellular module being used. For example, in cases where reducing the scanning time is necessary or preventing the use of a specific RAT is otherwise desired, disabling RATs that are not going to be used (e.g. 2G if only 3G/4G are desired, or Cat-M1 if only Cat-NB1 is desired) can slightly reduce the cold-start scanning time and force a module to use a specific RAT. Another example is if the specific cellular module being used requires an option to be manually configured in order to enable an operator-specific extension (I would recommend consulting the specific module’s documentation, especially for any Cat-NB1 operation, to see if this is recommended/required by a specific module).
In cases where a specific operator is required (i.e. due to coverage), it is good to ensure that the specific cellular module supports the radio bands used by the operator in that coverage area by consulting the cellular module or device’s documentation, as well as consulting said documentation for considerations when utilizing a specific RAT or extension. Currently, in all use cases (regardless of operator, automatic/manual operator selection, RAT, or extension) the cellular module or device should be configured to have its APN set to the hologram APN.