Is it standard proceedure for a court appointed lawyer to not contact you back when you call with a questions about your case?

Of course, it's not "standard procedure" but it happens all the time.  How many times have you called him.  If you've called him more than three times, and some time has passed since those phone calls, I'd send him a letter, via certified mail, and keep a copy for yourself.  And in that letter I would document the dates and times you called and the person you spoke with and the fact that there's been no response.  You should also clearly indicate in that letter all the phone numbers where the lawyer can reach you.  If you get no response to that letter, then you should inform someone (with proof of your letter) that you want you case reassigned. 

Court appointed attorneys are swamped.  This happens all too often.  But you have a case you need to get ready for.  If your lawyer won't return your calls try going down to the office.  Let them know you are not happy with things.  Ask to speak to a supervisor and respectfully ask to meet with your attorney if possible.  If not, you could then ask that another attorney be assigned to handle your case.  Chances are this won't happen since they are all busy but it couldn't hurt.  Either way the supervisorr won't want any headaches so chances are they will see to it that somebody meets with you or at least returns your calls. 

The lawyer may be very busy. However, when he has time, he should be willing to discuss your case and answer any questions that you have.