The problem I see with this isn't having to carry your phone around everywhere - its the biometric system itself.

Biometric systems are much less usable than passwords. Users often fail them by doing things like putting their fingers in the wrong place on the sensor or by not looking directly into the camera.

I think probably that users will need to be somewhat trained in order for this to work well. Probably the hackers will train themselves too.

Stealing fingerprints from someone at a bar? Not so farfetched.