I work part time in a call centre, and understanding Welsh people on the phone is immensely difficult I find.
I worked in a call-centre a few years back and was asked a couple of times if i was from the Blackburn area, don't know how they got that from my Beverley/Hull accent!
I can't honestly say I've ever found the Hull accent to sound particularly intelligent. Other parts of Yorkshirer maybe.... although certainly not over in Barnsley or up near Middlesbrough!