Which carriers work to send SMS

Hi All,

First off, I am a complete newbie with everything related to sim cards and mobile carriers. Please forgive any stupid questions :slight_smile:

I am designing a product with a very simple micro controller communicating to a NimbeLink cell modem with a Hologram sim card. The goal is to use this system anywhere in the U.S. to send occasional SMS messages. Communication to the cell modem is working well and sometimes I can send the SMS through the system (using “AT+CMGS=” command) but sometimes the cell modem simply can’t send the SMS. I suspect some cell carriers allow SMS messages but some don’t. Are there only certain carriers which are able to do this? If only carriers allow SMS messages, is it possible to configure the modem to only use those carriers?

Thanks in advance!

SMS should be supported by all carriers in the US. We have seen issues of sending messages between carriers, as in sending it to your phone on a different provider than what the SIM is on but sending SMS should not be an issue on any carrier.

Is it possible the message you are sending is not configured right? Like over 160 characters long or encoded improperly?

Thanks for the good information Dom. Sending the AT+CMGS= command works fine 95% of the time but occasionally the cell modem fails to send the OK response and the text message never reaches its destination. The same message of only 30 characters is being sent every time so it’s not a message formatting issue. Nimbelink tech support seems to think certain carriers can’t process the AT+CMGS= command. I’m trying to read the carrier information out of the cell modem when it fails but haven’t been successful yet. Let me know if you have any other ideas.


So doing AT+COPS? fails when it doesn’t successfully send a message?

The AT+CMGS thing sounds wrong… that’s a standard AT command and I have not heard of that being an issue on any US network. Granted that is their modem so maybe they know something I don’t but I can’t think of a single time we’ve come across that problem on a network we partner with, even outside the US. Its usually after the SMS has left the modem that it gets stuck or blocked at the SMSC level when we see issues. If I checked our logs I could probably find an SMS sent from every US carrier we’ve encountered so unless its roaming on some small regional provider that we don’t have an agreement with that response from nimblelink just doesn’t seem right to me.

What RAT is the modem? Cat-M1? we have seen issues with SMS on cat-m1 but thats more to do with how the modem and the towers are configured to handle all the cat-m1 things and usually they are not in harmony.

Sorry, let me explain this better. The cell modem is part of an embedded system which frequently power cycles (the modem is always disabled before power is cut). Every time the text transmission failed, the system power cycled so I wasn’t able to send the AT+COPS? command to see what carrier it was using.

I’m not familiar with RAT. Can you explain how to find this? The Nimbelink part # is NL-SW-LTE-QBG96 if that helps.

Thanks again!

Good thing I literally just copied a link to this wikipedia article haha

Sounds like from that part number its using a BG96 so it could be the CAT-M1 LTE or 2g fallback sending the SMS. Normally even after a reboot, modems tend to connect with networks they are familiar with/were just on, so while its not 100% accurate seeing what network it connects to after a reboot might give you a good hint at what network it was on. Can you do like AT+CEREG?, AT+CREG?, and AT+CGREG? I am curious what networks its registering on.

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