Is an Android phone with audio GPS an acceptable substitute for a dedicated GPS system?

I am starting a new job requiring visit to clients’ homes, meaning that I will need a GPS.
I have read that Android-based smartphones use GoogleMaps to give directions and that you can get turn-by-turn instructions from the phone.
My question is whether a GPS unit like a TomTom or Garmin is better suited to my purposes than a smartphone.
I gave up my Blackberry when I recently changed jobs so I am going to get a new phone anyway. I will be making about three visits a day, three days a week in areas that I am not really familiar with.

Thanks