How does Hologram SIM decide with which network it will connect?

I became interested in Hologram after reading that it works on the T-Mobile 2G network. I have several 2G GPS trackers for model rocketry and airplane use. As AT&T has discontinued its 2G service, these trackers only work with SIMs from TMo and TMo MVNOs. I tried the Hologram SIMs with the trackers but they are not working, even though the Hologram SIM is said to work with 2G. I assume this is because the SIMs detected a stronger AT&T signal and connected to it rather than to TMo. If so, I will not be able to use the Hologram SIMs for the purpose I intended. If there is a way to force the SIMs to connect to TMo rather than AT&T, please advise. I did set the APN to hologram but that did not help. I placed a Hologram SIM into an unlocked cell phone and it does work fine there, it connected to AT&T.

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Hi @billdz, thanks for the question.

Picking which tower to connect to is the job of the modem. Essentially, it will query all towers which are available and compatible with it’s antenna. The modem will store these networks in an array on the device and iterate over that array when it tries to connect. This is a simplified explanation but works.

AT&T no longer has a 2G network so your modem will not find or store AT&T in the available network array.

Our SIM is compatible with all the available networks in America as long as your modem and antenna support the network type. Also, your modem needs to allow for roaming when using a Hologram SIM. Some firmware needs to be manually updated to support roaming as out of the box they only support home networks (non-roaming).

Hope this helps.

Out of curiosity what hardware are you using?

Interesting, thanks for the reply. When you say “modem” I assume you mean something inside the tracker. If so, I wonder why the modem is not finding and connecting to TMo. I am not aware of any way to allow roaming, perhaps that is the issue. The APN can be set via an SMS command. I have several 2G trackers, the one I used to test the Hologram SIM is this one:

Any other thoughts? Can I somehow get my trackers to contact to TMo with a Hologram SIM?

I’m unfamiliar with this tracker. Your best bet would be to contact the hardware manufacture since they’re the only one who knows how their firmware works. You’ve successfully tested the SIM in another device so we can check off it being a SIM issue.

Hi Bill — We’ve been wondering the same thing, but also how does Hologram select which 4GLTE Cat M1 service to use between AT&T and Verizon in the USA?

After talking with both of these providers, as well as with other MVNOs that provide their services, we have been able to determine if we get a SIM for AT&T (from AT&T or an MVNO), that same SIM will also work with their 3G and 4GLTE Cat 1 networks (maybe other Cat x’s as well, but not sure), but that same SIM will also work with their new 4GLTE Cat M1 network as well. In other words, with a single AT&T SIM, we can plug it into several modem types, with multiple fallback and carrier scenarios. For example, an AT&T SIM will work with a MultiTech MTSMC-H5, which is a 3G/HSPA+ with fallback to 2G (which AT&T doesn’t provide, but some of their partner carriers still do, including T-Mobile). In addition to T-Mobile & AT&T, this same -H5 modem will also work with Aeris and Rogers. The same AT&T SIM will also work with a MultiTech MTSMC-LAT3 4GLTE CAT 1 module, which also has fallback to 3G (frequency bands B2 & B5 only), and the this modem will also work with T-Mobile (maybe others). The same AT&T SIM will also work with a MultiTech MTSMC-MAT1 4GLTE CAT M1 only modem (but no fallback, even to T-Mobile’s 4GLTE NB-IOT network, with this one).

However on the Verizon side, it seems you have to pick the modem type and SIM type together. A Verizon CAT M1 SIM will work with MultiTech’s MTSMC-MVW1 modem only, and that model modem will only work with Verizon. And vice versa, Verizon’s 2G/3G SIM will only work with MultiTech’s MTSMC-C2 model (but the -C2 will also work with Sprint and Aeris networks, at least until these carriers “sunset” their 2G networks, according to MultiTech’s datasheet

Therefore, it makes us wonder how Hologram can offer 4GLTE Cat M1 services for both AT&T and Verizon with one SIM, roaming or otherwise, and what if any APN or other changes are required to make it do so?!?


Two things that are not mentioned is setting the hologram APN to the the first position and setting the preferred operator with AT commands. I spent a month cursing a vendor, he asked his customers how they got connected then passed that information on since I wasn’t getting anywhere with hologram.

I would suggest a carrot to gets users to post connection success around the USA along with the commands they used, devices used and locations.

Hi KevinA — We have been told in recent weeks, by representatives of both AT&T and Verizon, that they have their 4GLTE Cat M1 network up and running on all of their (and their carrier partner) cell towers, and that their 4GLTE coverage maps also apply to their CAT M1 coverage in the USA. We’ve also been told that T-Mobile will have their 4GLTE NB-IOT up and running on all of their towers in the USA “by the end of the year”, and that they are also planning on adding CAT M1 after that. AT&T and Verizon have both said that are not going to implement NB-IOT at all.

I agree it sure would be nice to get feedback from actual users with real connection successes with Hologram SIMs (and AT&T and Verizon SIMs, too), along with specifics of which devices (modem chipsets), APNs, and commands were used to do so. We are using both the Pycom GPY (with limited success so far), which has the Sequan’s Monarch (CAT M1 & NB-IOT) 4G-EZ LR5110 Chipset.

We also plan to test with the MultiTech MTSMC-H5 (Telit HE910-D Chipset), the MultiTech MTSMC-LAT3 (Telit LE910-NA1 Chipset), and the MultiTech MTSMC-MAT1 for AT&T (and/or MTSMC-MVW1 for Verizon), which uses the Telit ME910C1-NA (-NV) Chipset.

Stay tuned — we will post our results as we find them out.


Hey @BillOtto and @KevinA,

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.

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Hi, HologramPat!

Thanks for the detailed response. If I understand you correctly, then if we have a CAT-M1 only modem module, such as the MultiTech MTSMC-MAT1 (or -MVW1), it is reasonable to assume it would be limited to scanning using the CAT-M1 Radio Access Technology only, and only on the frequencies supported by AT&T for the -MAT1 model (ie. 700/B12, AWS1700/B4, or 1900/B2), or by Verizon for the -MVW1 model (ie. 700/B13, AWS1700/B4). And we only need to worry about setting the APN to “hologram" — not specifically for AT&T or Verizon.

However, with either of those modems, we should only expect it to be able to get on both CAT-M1 networks, if the frequency available happens to be AWS1700/B4, which is the only frequency common to both carriers (with both the -MAT1 and -MVW1 versions). Furthermore, we could also assume it would be unlikely that both carriers would be using the same AWS1700/B4 frequency in the same geographical area.

This is a lot of assumptions by a CAT-M1 bystander, so please correct anything I said that is wrong or unknown.


Hey @BillOtto,

I think this is correct.

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