I keep my personal mobile on and it sits on my desk, however I have an office to myself so it doesn't intrude on anyone else.  I would have it on silent if I shared an office.  I have children and that is the contact number that I give to the school and childcare.  

Should it ring with anyone but hubby, my mum, school/childcare or doctor then I tend not to answer it but drop the call.  Having said that, it's rare that anyone calls me during work hours because everyone knows I work and so do they.

As for ringtones, yes they are all different LOL.  I cut some mp3's down to 20 second snips for each of my children, my mum and hubby LOL.  They are all tasteful.  My general ringtone is a snip from a Daft Punk/Kanye West track which probably isn't as tasteful

My work mobile has just a "ring" ringtone and it's on permanently.