Spallen and Feehily are from Ireland, Caldwell is from Northern Ireland, and Callaghan is American.
The 29th annual honor is given to an outstanding English language work by a female dramatist.
Judges for the 2007 awards included actors Jill Clayburgh and Deborah Findlay, playwright John Guare, The Public Theater's artistic director Oskar Eustis, London Financial Times chief theatre critic Alastair Macauley and U.K. director Anna Mackmin.
The previously announced list of finalists was:
Francine Volpe - The Given Playwrights Amelia Bullmore and Elizabeth Kuti split last year's award for Mammals and The Sugar Wife, respectively.
The honor has also gone to Gurpreet Kaur Bhatti's Behzti (Dishonour), Sarah Ruhl's The Clean House, Dael Orlandersmith's Yellowman, Susan Miller's A Map of Doubt and Rescue, Gina Gionfriddo's U.S. Drag, Bridget Carpenter's Fall, Charlotte Jones' Humble Boy, Jessica Goldberg's Refuge, Paula Vogel's How I Learned to Drive and Moira Buffini's Silence.
The Susan Smith Blackburn Award is named for the noted American actress and writer who died in 1977.
Plays are eligible whether or not they have been produced, but any first production must have taken place within the preceding 12 months. This year's finalists were chosen from approximately 90 submissions.