Imran,
It is a totally different experience in setting up a call center in Pakistan as compared to US. Yes you do require a license to setup a call center in Pak. Contact PTCL for that. Seconldy, do not go with either DSL or Cable. I would recommend Clear Pipe IP or IPLC, whichever you can afford. And thirdly, do not consider setting it up in Lahore, as you will have problems in finding agents. Islamabad is a more suitable and stable place for call center agents. If you have any further questions, please post them here.
Regards
– Harris