Is it proper to call the opposing witnesses a month prior to Trial to determine what they know and what they are likely to say?

Are you a lawyer and has this witness been deposed? If you are the defendant put the phone back on the hook and avoid being charged with interfering with a witness or worse.

No, the person involved in the case can not talk with the other witness. Your attorney can question them, can ask the other attorney to provide a list of witness, and all the evidence they are going to present

You personally talking to the other sides witness can help you lose the case or even cause criminal charges to be filed.

No, my attorney "withdrew" a couple of months ago because I couldn't afford to pay him.

I am (reluctantly) representing myself. All motions and court proceedings are sent to me directly.

Since we are scheduled to start Trial in a few weeks, I thought I should know what the other side's witnesses actually know about the Plaintiff's claims. His Interrogatories and Deposition contradict each other and he references the witnesses.

What should I do? (I can't afford an attorney at this point.)

Use the contradictions in court to show stories not same,