Though the following article from OpenDNS talks about changing the DNS hopefully it will point you in the right direction to see the DNS configuration for your device: Open DNS - Smart Devices - if not post back with the model name of the device or whether it is running iOS, Android, etc
Thanks for this - I've veen able to follow the instructions and check the DNS on my own phone but when trying the same thing on the new phone the IP address is shown as 192.168.0.7 but I can't worknout how to change it. The handset is a Vodafone Smart first 7.
The handset is running Android so the steps are (which I suspect you have already figured out):
From the Android Menu home screen, tap Settings
Tap Wi-Fi on the menu.
Long press the Network you're connected to, and tap Modify On some devices, you may need to check the box for Advanced to see further settings.
At this point if IP settings shows DHCP then the handset should be using Virgin Media's DNS however if it is set to Static then DNS 1 and DNS 2 show the IP addresses of the DNSs in use. If it is set to Static make a note of IP address, DNS 1 and DNS 2 values and then change from Static to DHCP and tap Save