I suppose a zillion of people have the same problem I have, and use GDT, and so have probably developped some simple ways of handling this:
I have a number of people/places to visit outside (both sales and service calls), mostly within 2 hrs drive from the office: for some the time/date is given by the clients, some I go alone, others with an employee, some are urgent some not, etc. I generally have a whole list of people I promised I would call them "when we plan to be in your area". Still, the number of calls is way too small for justifying a high tech system, but I feel the current highly intuitive system based on "OK I have to go there tomorrow, let's see who I could call in the neighborhood" is not efficient.
How do you people do that ? The informations are multi-dimensional (place, time constrains, who is coming) and quickly obsolete. One could do it with a map (paper or computer based) with labels, or start with the calendar ... does anybody have a good system and wants to share its insights ?