I'm currently tracking my field technicians through our dispatching software. It uses the GPS location of their iPad to display their location on a map, but it does not work if the iPad is out of data range or if the technician forgets to change his status from "driving" to "working". I'm switching to something that is vehicle based and can keep track of mileage for maintenance and fuel consumption. Leaning toward Argotrak right now but I'm interested in other options if anyone has a recommendation.
I use a system called iGotcha which is a CallPass product. CallPass may have other products that are better for your application. We put them on customer vehicles when they do a car loan with us. I have previously used units from a company called Goldstar. The Goldstar units are good but installing the iGotcha units is easier. I don't know anything about Argotrak but some light googling should help you compare.
We had the Verizon Hum system in our Verizon work vehicles, tracks mileage for maintenance and GPS for location history.
Verizon system is good from what I have heard plus you can put it together if your guys have company phones also.