Hi Sleepless,
There are two places listed that accept mattresses in Dallas here
search.earth911.com/?what=mattress&where...try=&province=&city=
Apparently the Dallas Furniture Bank will pick them up.
If you're on a social network ... a message to your friends may find someone who knows someone willing to pick it up.
Leaving it outside on the boulevard with a descriptive sign will often make it "disappear" with or without an accompanying craigslist ad.
If anyone else has any ideas I'd love to hear them. The less that mattresses end up in the landfill the better
Phoenix