After a couple rounds of cute Twitter flirting (Ri: "Its BRITNEY BITCH!!!! @britneyspears one of the biggest worldwide popstars! U gangsta #EPIC". Brit: "You ain't so bad yourself honey..."), Rihanna and Britney Spears delivered earlier this morning with a Z100 exclusive of the new Britney-featuring remix to Rihanna's smash hit "S&M." The song now features a new second verse sung entirely by Spears, as well as Brit trying her hand at one of the choruses, and joining RiRi for the final round of "like it like it"s and "S-S-S-and-M-M-M"s.

Brit is fairly game in playing along with the song's themes of sexual dominance and experimentation love-hate media relations, insisting "Tough, I don't scream mercy / It's your turn to hurt me" and instructing "If I'm bad, tie me down / Shut me up, gag and bound me." It's always a lark to hear the former Mickey Mouse Club tyke take a trip down to the dungeon, but despite all the Twit-banter (which in all likelihood was done by a couple middle-aged management reps wondering how their life ended up here), Britney's contributions sound distinctly like they were cut-and-pasted onto the Rihanna original, without much actual collaboration between the two. Plus, sex kitten (cat? cougar?) though she may be these days, Brit's voice still lacks the growl that Rihanna really sells the song with on the chorus, sounding neither seductive or demure, but rather just unenthused.

Still, we'll hold off final judgment until we find out if there's an accompanying video, natch. The possibilities abound.

For lots more pics, videos and up-to-the-second dish on Rihanna, check out her Popdust Artist Page.