I am using the Raspberry Pi 3G/4G LTE Base HAT with the EC25a Mini PCIe with Raspbian and PPP. Yesterday I was able to send and receive SMS text messages. Today I can only receive text messages. Attempts to send a message generate a +CMS Error: 350 which is not listed in any documentation. Would it be possible to get a complete list of error codes? It almost appears like the CTRL+Z character is not being received so the error could be a time out but no way of knowing without the error codes.
Can you test sending with another SIM?
Can you send SMS with this SIM in your handset?
+CMS Error: 350 can be caused from diffrent reasons.
1. Depleted call-up credits
This error was shown on prepaid sim cards with depleted call-up credits.
2. Invalid number
On a invalid number the modem delivered the same error.
Thanks for the additional information. I was able to verify that CTRL+Z is working using the AT+CMGW command which requires a CTRL+Z to write to memory. So I am thinking as you are that it is either depleted call-up credits or not supported by the carrier. I called US-Mobile and they claim that the Quectel EC25a is not supported by them (which sells T-Mobile). I had previously signed up for T-Mobile through their web site which redirects to Embedded Works to manage the T-Mobile plan but it doesn’t include SMS messages, only data. So probably makes sense that both T-Mobile resellers don’t support SMS. I think that leaves in USA for the EC25a either AT&T LTE-M or Twilio (which requires that I use their framework and not the AT commands). Do you know if AT&T LTE works with the EC25a for SMS? If so, I will order a SIM from them.
AT&T LTE works with EC25a for SMS.