Combine sugar and gelatin in a pot, and whisk in milk. Heat over low heat, stirring continually until sugar and gelatin are fully dissolved. Take pot off of heat.
Using electric mixer, beat cream cheese until fluffy. Blend in lime juice, then slowly blend in milk mixture until smooth. Spoon mixture into pie crust. Chill 2 to 4 hours until fully set. Top with lime slices and mint.