its just their short code. there are different types, CO put the disclaimer in there so that if your carrier bills you they've warned you (since only one of the top 6 carriers give you free incoming texts).
That is just one of the free short codes out there, one of the other popular ones is the google text, which is just as good as the CO one.You can text your flight number and carrier to them and they'll reply back with information. IE: "flight CO 2790" send it to "GOOGLE".