I remembering seeing a Google IO video stating that NFS Shift is exclusive to Verizon for the next 60-90 days. The only way to purchase it is through a link on the demo, but you have to be on Verizon's network for it to work.
I assume if you purchase through the demo it'll bill directly to your Verizon bill since only Verizon customers can purchase it at this time.
The rest of us will just have to wait until the exclusivity ends.
I got the demo work on my Vibrant and so far it's the best looking racing game on Android.