Hmph, that's odd. Maybe the OBiTALK server over-wrote the DNS server you entered locally. I haven't experimented with that.
Instead: try changing the DNS servers you use for your entire home network, to use Google's high-performance DNS. Log into your router, find the LAN settings, and change the primary DNS to 8.8.8.8 and the secondary to 8.8.4.4
Save the settings and reboot your router. Go back to the OBi's local web page, look at the DNS setting again, and see if it had reverted back to default. If it hadn't, then set it to default yourself, save the setting, and unplug the power and plug it in again.
Did that make a difference?