Hello @tmmke,
the baudrate and other parameters should be configured as decribed in the product information https://www.unipi.technology/unipi-neuron-s103-g-p107?categoryId=8
If you are using the latest Mervis IDE and Mervis OS 2.3.0, you do not need to worry about the setting the GPIO18, which is done automatically.
To send the SMS, you can follow similar tutorial https://kb.unipi.technology/en:sw:01-mervis:sending-sms-hidden
GPRS (internet) connectivity is not supported in Mervis and has to be done manually in the Linux as discussed here https://forum.unipi.technology/topic/463/s103-g-use-gsm-gprs-module-to-connect-to-internet/7
Note: The modem cannot send SMS and provide GPRS connectivity at the same time!