Get the device from Best Buy or online, plug it into your car, connect your computer to the network, open the web interface http://attwifimanger.com and verify that your system is working. I would change the security settings later.
Now call (866) 595-1222 as mentioned 2 times above. The person answering says thank you for calling Car Connect! It might take them a minute but tell them you want the Connected Car Unlimited Stand-alone $20 plan. They waived the activation fee (or will when I call once I receive my first bill) and I was up and running in about 30 minute.
This is NOT a 300MB plan. This gives you 22GB of high speed data. After 22GB you fall into a Network Managed speed plan. If the network is not busy you will remain at full speed. If the network will prioritize other users requests ahead of yours but the speed will either be the same with a delay or they may simply move you to 3G during times of congestion.
