Do you talk about the situation? And how much of is it contingent on the circumstances of their leaving (obviously a reference would be out of the question if the firing was for severe misconduct)?
In some states, the only thing you can do is confirm the employee worked for you during a time range. Saying anything else is actionable by the former employee. It is really important to know the law in your locale.
It is actually safest legally just to say your company policy is to give dates only. If you took legal action against the employee (e.g. theft) then the new employer will find it on a background check. Their failure to do a background check is their fault.
Anything negative at all, and a lot of positive things could be interpreted as partially negative, exposes you to risk if the employee doesn't get the job.
I am not a lawyer.
There are various ways to get around this when getting or giving references.
Outside of that, the best thing to is to confirm employment with dates. Oddly enough, some people will list a reference from where they were fired for misconduct. I'd bet that said person doesn't even understand what constitutes misconduct, why they were fired and how to avoid it in the future.
Call or email, leave a message asking to be called back IFF the candidate was exceptionally strong. Assuming you aren't a competitor, you'll probably get a call back if true. If the guy was meh, it is a nice way to pocket veto.
For when you do employee referrals, if employees are getting pressured by lames to refer them, let them do no-op referrals. Default bring meaningless, and "strong referral" being a real referral. Google, Facebook, etc do this.
It would be exceedingly difficult to successfully sue someone for failing to return a call or email from a random outsider. Plausible deniability.
This is also one of the cases where being part of a "mafia" is awesome -- you can actually call up and get unvarnished opinions, or at least, cagey "I don't think I would" "That might be difficult" etc.
Your suggestion would basically just screw over any person whose boss had more pressing matters on his plate.
I think it's quite amusing to see everyone saying the recommended advice is to just confirm dates and title. It is, but only if you're implying that you have nothing positive to say about the employee.
Potential employers call HR to confirm dates and titles. They call former managers/supervisors to confirm other aspects of a potential hire's work history, i.e., to confirm the potential hire's alleged accomplishments while working for your company.
There are laws in most states saying that employers cannot impair a terminated employee's post-employment job hunt. This does not mean you can't talk honestly about the employee to another potential employer if you're asked. It does mean that you can't lie about the employee in a way that harms their job prospects (legally, this includes exaggeration).
Think about it folks: if there were laws saying that you couldn't talk honestly about former employees, no one would ever ask for references, especially not corporate HR departments, because it would be illegal and they would be exposing themselves to serious civil liability. The law usually is logical, if you know what the logic behind a particular law is.
That said, I'm glad a lawyer is here to say that you're allowed to talk honestly about an employee's work history and that you're not limited to date/title/pay. That seems to be the most pervasive job-search myth I run into.