There must be millions of people do the same? They use the landline just for broadband purposes and 0845/0870 calls and they use the mobile for landline / mobile calls? The mobile is inclusive of minutes used where the landline would be charging before the deals come into effect in the evening/off peak.
If it was' nt for the broadband connection the landline/house phone would be obsolete and the iPhone4 is another step in that direction... Soon nobody will hold a phone to thier ear in the traditional way, everybody will "videocall" and wireless connections will be as fast and reliable as your landline/cable broadband...When the speed on the wired connection is slow and outdated the landline will be dead and the tone when you pick up the phone will be no more!
Coming soon I can see it....Ipad+iPhone Enabled LED Internet Enabled TVs! Use your ipad as a control/2nd screen for the TV with iPhone built in somewhere along the line.