Does your ISP blame BT for every problem you have? If your ISP is BT they will blame open reach and then crack on with resolving the issue. They all have issues, just one less layer of blame if your isp is bt.
Over the years working with Verizon, L3, pipex, cw, Vodafone, Ntl etc, it's always been easier getting a strait story from bt rather than the garbled regurgitated crap from the others hours after they've received their updates from open reach.
As you mention the cost of dialing a mobile number is something bt are wanting to address with ofcom.