Please note that operators require a different number format to which the SMS is to be sent:
Another problem with Vodafone prepaid SIMs may be that the new SMS must be activated, which only occurs when the first call is made from it. Unactivated SMS normally log in to the network, but SMS from it cannot be sent.
If the GSM modem is disconnected from the power supply and reconnected, it is no longer able to establish communication with the IPLC, which is still connected to the power supply and the SMS no longer goes. Tested several times on GSM modem Cinterion TC35i and IPLC300.