I know it's sometimes tempting to call the annoyance callers back but this Spanish caller leaves a voice mail for me and if you listen carefully, you may understand that she is talking money and your cell phone and charging your account for whatever rip-off they are attempting to get away with; and since there are ways for con artist to steal money from you by charging your cell phone account -- and there is likely no way you would ever be able to recover the stolen money -- it is risky for you to call them back, as this would be the way they would be able to trick you into saying the wrong thing or pressing the wrong button which they would claim as giving your permission for the charges on your account. So I would recommend that instead -- add their number to your Contacts List and set the number up with no ring tone or vibrate or whatever your cell phone will allow you to configure for that number.
And this problem always causes me to ask the cell phone and software designers this question; why the hell haven't you people created a way for cell phones to BLOCK annoyance calls permanently...? We should not STILL be having to deal with this sort of crap in the year 2010. Our cell phones, inboxes, mail boxes and voice mail boxes are all paid for by their Owners and are PRIVATE receptacles for the things we order and request from others and they should have giant *No Trespassing* signs posted at their entrance. No one should be able to call us to sell us something without our Permission. I've never bought ANYTHING from ANYONE on the phone -- and if the rest of you would STOP doing it -- they'd all eventually have to go away. When there is no profit left in it -- they will stop and hopefully go out and get real jobs.