Has anyone tried this cellphone based monitor?

[tangomar]

It requires OBD-bluetooth, so not very cheap solution to start with but the software itself is only $20.

Auto Mobile - OBD software for cell phones

[dcb]

MAF vehicles only for the mpg readout, doesn't sound like a very robust mpg algorithm. Don't see the concept of a "trip".

Playback could be useful, bit of an expensive solution though.