How long should one wait before returning a call?
I feel that unless there is no way for you to get to a phone or retrieve your messages (which rarely happens, especially in this age of cell phones), 48 hours is the maximum time that should go by before a phone call is returned.  If you know that you will be swamped and unable to talk, give a quick call to the person who phoned you and let them know that you are going to be very busy over the next few days, but would love to catch up after that. 

How many times should one try to contact a person before giving up?
Don’t ever give up.  If you would like to speak to someone, I would call sporadically, without stalking them, until you reach them.  Keep in mind that they may be on vacation or away on business.  Also, leave the reason you are calling on their machine and perhaps that will give them incentive to return the call. 

Should one attempt to discuss the problem with the person she has been trying to contact? 
This depends on the relationship you have with that individual.  I have encountered individuals like this and have had discussions with them regarding the situation.  I have politely asked that they please have the courtesy to return the phone call, even if to say that things are busy and we will catch up at a later date.  Try to have this conversation when you are not feeling angry about the situation.  Explain that you too have a busy schedule, but would like to find a convenient time where you can talk.

More Quick Tips:
Business Telephone Calls	Proper Introductions
Email Etiquette	Business Meetings in the Home
Are You Busy?	Life In Your Home Office
Unexpected Payments: To Accept or Not to Accept	When Your Healthy Home/Work Life Balance Is In Jeopardy
Dealing with Difficult People	Equal Share
Returning Phone Calls	Handling  Little Awkward Situations
Call Waiting Etiquette	Should I Take The Blame?
Networking Dilemma	It’s Not Your Job Title That Is Important….