adding contact management

The Nav Dynamics classic we are currently using has major modifications done. I am looking to add contact management has anyone added this after being on the current system and if so any issues. Because we have so many mods in our system will we have issues with out of the box contact management. I really do not even know if this is what i am looking for but need a tool to help sales team follow up on leads. Can’t really find much out there to give me an over view or demo

Any suggestions would be great. Thanks KG