Problem with DNS connection

Hi!

I have a problem on my iphone 3GS and iPad2 for DNS connectivity.
I have read to many comments about changing DNS to 8.8.8.8. It was worked with FaceTime and push notification. But, it doesn't work for Appstore and Facebook apps (stuck in loading page). I have to switch DNS back to 192.168.1.1, then they can be connected again, but facetime doesn't work with this DNS. Now, I have to switch between two DNS. I don't know what's the cause because everyone can use 8.8.8.8 with all apps.
My router is D-link DSL-2640T (already forward port) and Itunes is up to date.

Please help me, if you can figure it, you are gorgious...
Thank u very much....

The address 192.168.1.1 is the default IP address of your router and has nothing to do with DNS settings. Where are you setting the DNS addresses at?

Any good public DNS address should work. The 8.8.8.8 and 8.8.4.4 are the public DNS addresses for Google. You could also try OpenDNS 208.67.220.220.

I changed DNS on my iPhone and iPad, also change on router on both 8.8.8.8, and 208.67.220.220, but AppStore and Facebook cannot connect too. it seems that I cannot use other DNS except 192.168.1.1, but this DNS doesn't work with FaceTime.

Please help me, thank u for your kindly help.