In my opinion DNS are best left to automatic but if for some reason you want to specify DNS then below is the list of DNS run by PTCL:
For PTCL users the Google DNS option is also pretty good and the DNS IP addresses for Google DNS are:
Open DNS is also an option be I personally find PTCL's own DNS faster and more reliable and my second preference is Google DNS.
If you know about more IPs for PTCL DNS then please feel free to add here in your replies and I will keep updating this thread in future.
I hope this helps a few people who are looking for information on PTCL DNS. Please dont forget to hit the Facebook like and G+ at the bottom of this page.