Photo of my Lumia 925 and Moleskine.
I DRIVE THOUSANDS of miles every year using Nokia Maps verbal guidance and over the years I have learned several quick ways of verifying whether my handset is up to the challenge.
If you buy a new mobile phone and intend to use its GPS, you should take your unit outside and see how long it takes to lock onto satellites in open air. You know you have a problem if more than 30 seconds elapse before lock-on. The problem could be nearby electromagnetic interference. Or it could be a weak GPS unit. My best units achieve lock-on within 15 seconds.
With my Nokia 925 handset (in the photo), the green button finds my actual physical location. If you know where you are and the green button is more than 100m away, you will encounter navigation problems en route. Those may occur as the navigation arrow jumps around on screen, often rotating into the opposite direction from your actual movement. This would occur with poor antenna sensitivity and if it happened to me, I would hesitate before replacing my handset with a similar one from the same shop. You might see the same problems if your unit was assembled during a faulty manufacturing process.
In my experience on European motorways and American expressways, Nokia Maps work well without assisted GPS. This saves me a minimum of 100 Euro a week while roaming in other Telco networks.