can i setup PPTP VPN connection in OBi200 admin panel?
No you can not setup a PPTN VPN connection in the OBi200 admin panel. If you want to run over a VPN you will need to set that up in your router or thru internet connection sharing thru your pc. I believe 3-party router software such as dd-wrt and tomato supports setting up a vpn.
If the blocking is just by port numbers for traffic going to your voip provider there are voip providers that respond to alternative port numbers instead of the standard. Of course on the OBi you can receive traffic coming to you on whatever port number you wish to configure.