FileMaker is an interesting app :) It started as an end-user tool and it still is one of very few database apps that a non-programmer can actually use. But somehow FileMaker developers managed to make it very scalable. There's no other platform where one can start with a useful tool and end up with a client-server app that for the whole company. In old days they used to have a splash screen that captured this very idea (I only found an imperfect version):
I.e. something as simple as a file cabinet that can grow quite big.
All FileMaker pros and cons come from its origin. As an end-user tool it's very much unlike other DBMS apps. No SQL. No real programming: scripts are basically macros that repeat user actions in a slightly more general way with variables and some logic. Lots of limitations; e.g. a list view cannot have a sidebar; a dynamic value list is always sorted alphabetically; to open a Save As dialog and read back the file name you'll need a plug-in; and so on. For a programmer this can be very frustrating, because most his assumptions will be wrong. And existing apps written by non-programmers are not exactly paragons of clarity and solid design.
But if you manage to overcome the obstacles you'll find a rather good RAD for client-server, single-user, web, and mobile apps, that stays rather usable over WAN, with such niceties as runtime and kiosk mode.
Having said that, I'm not quite sure about generic contact management and scheduling apps in FileMaker. If this is what they are, then they should be unlocked, so the customer can make changes; or they have to be niche apps that do for the customer what nothing else does.