I still recommend trying openDNS or google's DNS servers first. You could also try a VPN external to Turkey. These options don't require jailbreak.
Originally Posted by Antarktikali
Otherwise if you MUST bypass DNS - here is how to do so.
SSH into your jailbroken iPhone (remember to also change the root password to prevent virus/worms infecting your iPhone via SSH)
As root run:
The IP address might not be right - you need to check this but I just tested this command on my iPhone and it added the line correctly. You also might need a few more lines to cover all youtube related addresses.
echo "188.8.131.52 www.youtube.com" >> /etc/hosts
To remove this (when they eventually lift the ban) run:
cat /etc/hosts | grep -v youtube > /etc/hosts