"Are you a swing singer?"
The icons of swing and jazz singing have impeccable timing and phrasing.
It is not essential to have an amazing vocal range or technique to sing jazz, which makes it great if you've never sung before. Singing jazz standards is about exploring the unique qualities of your voice and learning how to personalise a song. Your jazz singing voice should be a natural extension of your speaking voice.

The best way to begin is by immersing yourself in the music of the great singers. Some of the best females include Billie Holiday, Ella Fitzgerald, Sarah Vaughan, Carmen McRae, Betty Carter and Peggy Lee. Male jazz singers to listen to include Nat King Cole, Frank Sinatra, Mel Tormé, Louis Armstrong, Joe Williams, Tony Bennett, Jon Hendricks and Mark Murphy.

Swinging. 
The other fundamental aspect of jazz singing is being able to swing. To get into a swing feel, start by stressing the off-beats in everything you sing. When singing in 4/4 time (ie 4 beats in a bar) in classical music the stress tends to be on beats 1 and 3 whereas in jazz the stress tends to be on beats 2 and 4.

Try saying "1, 2, 3, 4" while clicking your fingers on beats 1 and 3, and then on beats 2 and 4. Beats 2 and 4 are known as off-beats, and by stressing them we get closer to the essence of swing. Now try singing any familiar standard, such as All of Me by Gerald Marks and Seymour Simons.

To help the song swing, click your fingers on the off-beats (2 and 4) as you sing. Now try stressing the off-beats with your voice. For example: "All of me, why not take all of me. Can't you see, I'm no good without you ..."