Free line offer via text. Legit? Limited time? Commitment req?

Got a text from 833-579-2247 saying I can get a free line "via bill credit" w/$10 connection charge. Seems legit source, but I'd rather not waste time if it requires of years commitment or something else scammy.

Anybody try to redeem this offer? Is it legit?

Forgot to mention I'm on "Unlimited Freedom" plan from Sprint.