Southwest Airlines, once known as a no-frills airline, has now become one of the carriers giving travelers the most frills included with their tickets. These days, when even free peanuts are considered a luxury, Southwest will eliminate transferability of tickets.

I think you can call it a “frill” if an airline ticket includes something that most airlines only include for an additional charge. Southwest certainly still has some frills — free bags, peanuts, and no change fees. (Although you do pay the fare difference for changes, and the airline doesn’t allow standby.)

One of my favorite Southwest “frills,” however, is about to become a relic of the past: transferability of airline tickets.

Although many travelers haven’t realized it, Southwest tickets have indeed been transferable. If someone purchased a ticket, and could not use it, they have been able give the credit to someone else. This has meant families and corporations alike aren’t stuck with tickets they can’t use. if someone has planned to visit a friend and can’t travel, they have been able to cancel their ticket and have the fare applied to their Southwest credit. They could then give the credit to the friend to come visit them instead or for any other flight.

Of course, this hasn’t meant that the transferee can use the same original fare, the credit has to be applied to a new ticket. But it’s still been a generous and useful policy.

Starting with tickets purchased January 27, 2011, however, tickets must be reused by the original traveler. On the bright side, Southwest isn’t instituting change fees. Yet.

No word on whether this would have happened anyway, but it’s possible the change has to do with Southwest’s proposed purchase of AirTran airlines. If so, ironically it will be merging with the Atlanta-based carrier that results in this “frill” being “Gone with the Wind.”