Hi back,
thanks for your info and sketches. Don't know anything about Seedstudio, but in fact, there are some tools using AT commands on the web.
In the meantime I decided to switch to to Arduino DUE using SAM 3X8E core, FREERTOS and implementing another library I found:
https://github.com/renzbagaporo/quectel-m10-sms-lib
The original Ardunio GSM library seems to be too big for my purpose, and furthermore, sometimes the dial-up just doesn't work, so after reset dial-up finally does its work. But frankly, this is not my goal.
I need a lean software library that reliably operates as requested, without "dead lock" or similar.
First I have to re-pin the GSM TX/TX connections to a real UART (in this case UART1) and no "software UART".
Greetings, Peer