The Activation Fee will be charged in month that you activate your device. Supposing that on 15th day of the current month you active 100 devices and on 20th day you active more 10 devices, your bill of the current month have the 110 devices in the Activation Fee.
In case you disable one device and activate in the same month, it will be charged only one activate, all reactivations made after billing will be charged as a new activation.
Monthly Device Fee:
The active device has a monthly fee charged.
In case an update package is sent for a device, a update fee is charged. The devices which did not fetch updates, do not has corresponding update fees charged.