hi
limesdr mini does not have a onboard-clock which is good (precise) enough for gsm requirements. there is no input which can easily be used with an external source like a gpsdo. thus there is no realistic way to reliably do gsm with the -mini, sorry.
limesdr-usb with external 10mhz gpsdo or lime-net micro should work.
i haven't done any specific tests with that hw lately.
kind regards