Don't know if this has been reported yet, but if I am running the phone on wi-fi using either my router at home or my network at the office the problem doesn't occur. As soon as I turn off the wi-fi the problem returns.
Unfortunately there is no wi-fi on the road so using navigation is next to impossible. It may work for ok for a few minutes at a time, but most trips are longer than a few minutes.
Have contacted my rep for a replacement. We will see what he says.
I hate to say it but an iPhone is starting to look more attractive.