Cellcontrol (https://www.cellcontrol.com/) blocks and phone from receiving or sending texts. It works with a phone app and a device that installs in the car to detect motion. You do have to buy the device for $129. This has additional features. You can log on to the website to see if the device has been disabled, how fast they are traveling and where the car is at anytime.
Sentinel: (https://www.drivewithsentinel.com/) Is one of the most expensive options but has lots of features. The cost is $249 per car and $25 per month. With this service you get a text if the person tries to use the phone while driving. You can also get messages if the car leaves a designated zone or is out later than allowed. It will also give alerts to the driver to remind them to turn off the phone.
Drive Safe Mode (http://drivesafemode.com/) is free. This ap uses the phone to determine motion. If the phone uses text or and mobile ap while moving you can be notified this is happening.