I'm all for an idea for this. Hell they could even charge me for the app if they're concerned with losing out on the fee for the physical authenticator. There are quite a few reasons why this is a great idea:

* Don't have to keep track of the physical authenticator. It's kind of small and one could easily lose it, plus it's just one more thing on my keychain.

* Don't have to worry about battery life. The physical authenticator will, albeit a long ways away, eventually run out of power. When this happens, you're kind of SOL if you want to play the game until you get it cleared up with customer service.

* It's on a mobile device that many people carry around with them all the time. It's one less thing people have to keep track of.

However there are some cons:

* It's on a mobile device, so if for whatever reason that device is rendered unusable (broken, out of power, stolen, etc...) you have to go through the same hassle as if you lost your physical authenticator or if it ran out of power. At the mercy of customer service until you can get it straightened out.

* It takes up space on your mobile device, I guess lol.