VZ Nav is a great application, but unfortunately it does have one glaring draw back; it does not work without some type of cell cignal. It will not continue to tracking your location when you're out of range. Though it will still display the map and your last known location. VZ Nav has had known issues of compatability with certain bluetooth headsets and audio transmission. It's best to try it out on your specific device first; there is a $2.99 option for 24 hours of use so you can test it out.

 VZ Nav does not incur airtime or megabyte charges to use, it will only cost you 1-2 megabytes to download the application initially. So for $9.99 a month it is unlimited use. 

Personally, I love VZ Nav. It does great in major citys like New York, Chicago and LA. It's awesome to be able to look up a restaurant and be able to go directly to it. I've found that it doesn't work too well in rural areas or mountainous areas; 1. because of signal issues and 2. because those types of areas aren't frequently updated. 

Also, you might want to ask if Verizon can move you to the 550 minute plan for $59.99, instead of your $69.99 for 700. That $10 you save can make up for using VZ Nav. 

Good luck.