I do not have a combined bill, I called to get the AT&T discount around a year ago. There is no more combined billing, just the discount. The AT&T discount does not extend the contract. Well it should not, it seems like you get a different answer each time you call DTV about nearly everything. On my DTV bill there is a line for the AT&T discount. The HD discount should not interfere with the AT&T discount, but we'll see what happens in the next few billing cycles.