Sending track points via the Iridium satellite network requires an active subscription, As do messaging and SOS.
In theory, the local track log (which retains the track on the device rather than sending it via satellite) does not require a subscription. You may or may not be able to configure a legacy device to do this. I no longer have an active legacy device, so I cannot test this.
Edited to add: Newer devices WARN you about this on boot. I don't know about legacy devices.
