Its my policy to always refer these callers to Fred.

Use Google voice numbers with a voicemail to screen calls asking caller to leave name, number and address of property they wish to sell.  

It looks to be affordable and they can email you the entire conversation that they had with the caller.

If you don't have a pen and paper - you now have their caller ID - do a preliminary bond and rapport session with them, go through a little discovery and tell them a time that you'll call back (then stick to that time!).

Screen caller for motivation to sell.  30 , 60 or 90 days out from being ready sell?

. :)I'd leave it alone.. take the next caller.. 

I say well I'm trying to schedule showings, I have some other's looking so depending on that I'll get back to you to set a time. and either I decide to call them back or work with the next caller that has a more defined time line to what I need...

If you include your rental criteria in your online listing, you'll waste less time pre-qualifying every caller / prospect. 

I have a team of cold callers and our biggest issue is getting more and more numbers each day.

Yes, some callers will not leave messages as well but return them as soon as possible