Do you already have experience with Osmocom and tried it with a phone ?

No  i haven't ,  tried  Osmocom with a phone yet, i have C139 and C117 available, once i tried but it reach up to downloading finish (of binary in firmware folder).  after that it keeps in that state for quite some time and shows download NACK  after wards, something went wrong , then operation aborted. i tried many times with it. As  i don't have much experience with HDLC or serial communication to UART, some binary files even do not download completely and receive FMTOOL abort.. while downloading   I'm using prolific USB serial DATA cable ( seems very noisy) but no choice as my notebook doesn't have a serial port  :-(     I'm thinking to assemble new PC though.   I need you kind suggestions in this regard.

What exactly do you want to do ? Only receive voice traffic ? You want to switch to an ARFCN and timelslot and listen to the voice traffic ? Of course this only works if the channel is not encrypted or you have Kc for decryption.

Yet again if i'm able to run the code  and even able to interact  using L2/3 or osmoload with phone i don't know how to use phones analogue BaseBand ( ADC) and download the fetched raw data after (  (of desired ARFCN n TS) to host PC and save it in  *.cfile format or MatLab( simulink) supported format , if i'm able to do up to this extent i'm pretty sure i can convert it into Voice as i'm reasonably sound with MatLab...   Of course , the TCH/F should be  without encryption, but i will create a interface  in MatLab codes to supply Kc , if available,  for future use. ( for digital BB processing )

What about frequency hopping ? Without knowing the hopping sequence its not possible to follow a hopping channel.

Though i'm not die -hard with C or C++ , but rather fine.  have previous understanding for implementing frequency hopping in ISM band, have seen protocol analysis using wireshark we can can easily extract hopping  sequence and and chase it ,  big problem is not to tune PLL synthesizer, but Time slot. and collecting the buffered data for processing , for this i have clear vision, i will share my source codes with you  once finish my work.