That could work fine, but dedicated GPS tracker hardware isn't that expensive and will be more robust and reliable than an old phone (simpler software, heat and

That could work fine, but dedicated GPS tracker hardware isn't that expensive and will be more robust and reliable than an old phone (simpler software, heat and vibration tolerant) - plus there's usually IOT-NB/LTE Cat-1 support so you can use less expensive cellular providers and most trackers have at least one dry contact output for remote immobilization. The main downside to hardware GPS trackers is that they're mostly sold "to the trade," so you get a reference manual for their often AT-based communications protocol and you're left to your own devices. There are open-source backend servers around but I feel they're often too genericized to work well with the features of any one tracker, so big incentive to write your own software.