I don't really listen to pop but from what I've heard so far it would be either Celine Dion, Adele, Rihanna, Debbie Harry (Blondie) or Amy Lee (Evanescence) That new singer Lorde also has a pretty sexy voice as well as Jen Ledger from Skillet.
Mercedes Arn-Horn from a band called Courage My Love. It's not that her voice is sexy (I guess it kinda is) but it's just sooo gorgeous to listen to, her tone is absolutely beautiful. Her voice is waaay more beautiful than anyone you listed (no offence). The only people who can come close to her are Hayley Williams (Paramore) and Marissa Datolli (Crystalyne). I mean, that's my opinion, of course.
Taylor Swift is pretty sexy, but as the first time I heard a song by her I was watching a video, I can't tell if I really found her voice sexy, or it was just that terrific face she has. Anyway, she's beautiful.
Can i mention guys' voices 🙈 If so there is Hamed as lead singer in mashrou' leila (fasateen, inni mnih, little watan) Damien rice (cheers darling, accidental babies, woman like a man...) Awolnation (sail)
That update needed posting, I worship Joan Jett and Stevie Nicks has a beautiful voice. As for a sexy voice, I feel like Joss Stone and Janis Joplin (R. I. P) need mentioning and Amy Winehouse (R. I. P) made everything sexy.