Some dodgy info there I'm afraid. Only BT Openreach can physically install new lines and will charge £88 + VAT. However any provider, not only BT retail, can approach BT Openreach on your behalf and will charge you whatever they deem fit. If Sky want your custom they will arrange a new line for you.

Currently BT retail offer free installation - http://www.serviceview.bt.com/list/public/current/Notice09_boo/2-FrameworkImpl337855.htm (offer extended til end of year) , 18 month contract and make a certian number of chargeable OR inclusive(free) calls. You can then choose whoever you want for broadband.