Yup. Last year I worked on such. There are some thousand devices but where folk lose their cool seems to be in either the device cost or the monthly cost.
The cheapest DIY system I use is an android phone. Great for those one off systems where your client thinks they have a "new idea."
The problem: I need to track a bus from city to city in real time.
I'm thinking of a gps device without screen or apps, it only sends the current location to a server. Is this possible? What device can be useful?