Army recruiters, what MOSs are being filled for prior service (my son is currently serving in national guard).

Just speak with a Army Recruiter in your area. If you do not know. What city are you in and I can let you know from there. I only handle physicians, nurses, pharmacists, etc

E-1 to E-4 with less then 36 months of Active Time can enlist RA as long as he has a 368 from the unit. He would first need to speak with his COC and see if they are on board to release him. Then he needs to speak with a recruiter to get entered into the system for the 368 to be generated or the recruiter can hand jam a 368. Also a 4187 has to be done, which states other criteria the soldier must continue to meet prior to shipping to their gaining unit. Once all the I's are dotted and T's are crossed. The Soldier must go back to MEPS to pick their job for RA. Sometimes the Soldier get's lucky and is able to stay in their MOS or they have to pick what the Army is looking for right now based of their ASVAB/Line Scores.

Look up USAREC business rules. I know Linguist, and Recruiter are open for prior service without Airborne, but with Airbone qualified he'll have a lot more options. However if he's still on his initial enlistment contract he can join active and switch jobs as long as he meets the line scores, GT, and all other deciding factors for the MOS of choice.