Knowing the SIM card serial no. is no big deal, but it shows these guyz may be having access (or might have worked or have supplied SIMs) to Qtel. afterall, Q tel must be having records for which mobile number what numbered SIM is issued.
Many of us have got such calls (miss calls) from this gang and it seems to be an organized one. I'm sure they may even be reading us in QL.
For us best way is to not get lured and for Q tel to bar these numbers.