Because many pediatric subspecialists are either hospital based (making it difficult to also do a primary care pediatric clinic), or academically affiliated (requiring they do teaching of residents, med students, and be active in research), it's often difficult to practice as both a General pediatrician AND a sub-specialist. I have known a few though. Many people in Developmental/Behavioral Pediatrics and Adolescent Medicine can do both general and specialty practice since they are pretty outpatient oriented to begin with (I plan on doing both as well). I know many docs in Peds ER who do locum tenens work for pediatric clinics in between their ER shifts. Most of the other organ system based specialties though usually get so much business with inpatient/outpaitent consultation it's often impractical to practice both (but still re-cert for both the general pediatrics and their specialty boards).
Nardo