@catalin ok. thank you very much for your detailled explanation at this time.

@jmarcelino I am trying to use LTE M1 connectivity in Switzerland with Swisscom SIM, but the attach() function returns False always (for hours). Swisscom confirmed that the network is live (band 20) in the area. >>> lte.send_at_cmd('AT+COPS=?') '\r\n+COPS: (1,"22801","22801","22801",7),,(0,1,2,3,4),(0,1,2)\r\n\r\nOK\r\n\r\n+CEREG: 4\r\n' '22801' is the PLMN code for Swisscom. So from the above result, doesn't that mean the Pycom module is able to find the operator? Has anyone had success with just lte.attach() with Swisscom SIM? If anyone is using Swisscom SIM for LTE M1, could you tell how you are connecting it?