Combine first 4 ingredients in a heavy-duty zip-top plastic bag; shake. Add chicken, and shake well to coat; marinate in refrigerator 2 hours, turning occasionally. Remove chicken, reserving marinade.
Cut plums into quarters. Thread chicken and plum pieces alternately onto 4 (12- inch) metal skewers.
Place skewers on grill rack coated with cooking spray. Brush skewers with half of reserved marinade. Grill 5 minutes; turn and baste with remaining marinade. Grill up to 5 minutes or until chicken is no longer pink in the center.