As this is for work, I'd also like to be able to be reminded of who within a group of contacts (potential clients) I haven't had contact with in a while.
It would need to run on Windows and a smartphone with decent input (hardware keyboard or Swype), with syncing possible both via cable and via the internet. Open source would be nice but I don't mind paying up to $100 for something that works well.
I had this (sans calls) running on my old Psion 5MX and Act! But I don't seem to be able to find a modern version.