i also looked into security options a couple years ago, below are my 2¢

the iphone is a good idea... but there is a slightly better solution
use an old ipad mini with cellular data plan

the ipad is better than the iphone for tracking application in almost every way
- most carriers let you get a second data plan sim on your existing cell plan for as little as $10 or about that area
- it CANNOT make or receive cellular calls and text messages (it will do imessage but that's not important, don't enable imessage on the ipad when you set it up)
- it won't get called and spammed potentially interfering with it's intended use
- it has a much larger battery for when your truck battery runs low
- it has better reception due to larger antenna volume
- with an ipad you can take a peak whenever you feel like it to check all is well, you can't check in on your truck just for fun with a lojack
the down side is it's bigger to hide in the truck, but an ipad mini will fit well on top the glove box


lojack looks nice on the surface, but check coverage in your area first, you maybe disappointed, call your local police and ask about lojack before buying it
also lojack is not available in Canada anymore according to their website.
with lojack you also must let their tech install it in your precious truck, it is out of policy for you to do it yourself or be present while it's installed in it's secret location (often on top the glove box)

your ipad will work everywhere your chosen data plan works,
i suggest checking out TMobile for this application because they told me they would do unlimited data worldwide for $20 more on my cell plan.
-s