An implantable infusion pump system is disclosed. The pump system preferably includes an implantable pump and a removable module. The module may provide for varying flow rates of fluid being dispensed from the pump or may provide for a constant flow rate of such fluid. In the case of varying flow rate capabilities, the module preferably includes one or more sensors to determine information relating to the flow rate, electronics for analyzing the flow rate information, and a mechanism for physically altering the flow rate. Methods of dispensing a medicament to a patient are also disclosed, as are variations of the pump system.