The Chase BA VISA offers a companion benefit for award tickets (mileage redemptions):

http://www.britishairways.com/travel...2/public/en_us

Discussion here:

http://www.flyertalk.com/forum/miles...lly-worth.html

Some other credit cards have offered a BA companion fare program for purchased tickets, but the paid ticket is for a full unrestricted fare.

No airline offers two deeply discounted tickets for the price of one. Typically, airlines offer a substantial discount if the customers buys a ticket which meets certain restrictions (e.g. advance purchase, change fees, no refund, minimum stay, etc.) Companion fares are another way to qualify for similar discounts without meeting those qualification, but they cannot be combined (except, perhaps, as part of a very short therm promotion.)