* What are the connection charges for Optical fiber line ?
Not sure. You can search the PTCL DSL thread and you will find the answer there.
* Are the tariffs same?
Yes the call rates, DSL rates, etc. are the same. Not sure about line rent.
* How do I apply for Optical fiber line
You have to go to your exchange for that. They don't take these orders on Helpline. (They might even ask to write an application).
Yes, the numbers are in different series as compared to (copper cable landlines).
Why do you need to install/switch-to ONU? If DSL works on your Copper line then you shouldn't switch.
IPTV service is not available on ONU.
I believe that you can't install any other company's DSL on ONU, you will be stuck with PTCL forever (correct me on this if i am wrong)
However, if you are having troubles then ONU is better. Optical Fiber is a far better medium for communication!