I'd had an HTC Eris. Traded up (?) to the iPhone. I'm a bit of a GPS power user - junkie, if you will. Not an expert, I just get a LOT of use from it. I loved the Google Navigator on the Android phone, and while not perfect (I've yet to see any GPS unit, software, or app that is) it was very dependable and accurate AND was included with the OS and integrated neatly into nearly everything on the phone that had any type of address in it.
Browsing through Apple's app store on my iPod Touch, I'd seen screenshots of the UI for MotionX Drive and was just drooling over its features, so I was chomping at the bit to get my hands on the iPhone and that was the first app installed, once I got it.
From the first use, I noticed it would occasionally lose GPS signal. The iPhone resides in the same mount, in the same location that the Eris did. I repositioned it to get it farther down the windshield and away from the roof of the vehicle, more. No change. So here are the steps I took to troubleshoot:
Installed and tried Waze, Mapquest, VZ Navigator, and Skobbler. They all exhibit the same problem. They lose GPS signal every 3-4 minutes for about 15 secs to a minute (sometimes longer), then it returns.
Tried turning off location services to everything but the GPS app that I was currently using - no change. Tried uninstalling all apps that use GPS, rebooted phone, went to location services and disabled it for the native maps app, the camera, and the native compass, reinstalled MotionX, rebooted phone once more, turned on location services just for MotionX, tried it - no change.
Called Verizon customer support. They couldn't help so they patched me through to an Apple rep who insisted it had to be a faulty app. I asked, "So, you're telling me that five different app developers wrote the same faulty code into five different apps?" His response was for me to contact the app developer. I did (MotionX). They responded promptly and told me they hadn't seen any issues like that, at that time.
At this point, I figure the process of elimination means a faulty OS loaded on the phone, or a bad GPS chipset. I take it to the Apple store and they do a DFU (I think that's what it was called), essentially wiping the phone clean back to its original state with a clean install of the OS. I load MotionX, and only MotionX, while still in the store and tested it on my way home from the store - it does it, again.
I go back the next day, they graciously swap the phone, with apologies. I do the same thing as the night before with one exception - I realize that there is one other common denominator - the Belkin USB power adapter that I'd been using all along. So, without plugging it in to the vehicle power adapter, I use MotionX running on a full battery charge and... yeah, it does the same thing.
All three times I dealt with an Apple rep, they asked me if I had a good 3G signal because they said the GPS has to have that to work properly. Most of the time when the problem occurs, I have good data signal. Also, if what they are saying is true, then the apps which store the map data on the phone (Tom-Tom, Navigon, ?) are worthless, so I have to call BS on that one. All the apps I've used have acquired a fix almost immediately, they just intermittently lose it, thereafter. My understanding is that the initial fix is where the 3G signal helps. I also understand that Verizon's technology only allows for connection to one cell tower at a time, so that means no triangulation and very poor accuracy for navigating.
Here's the kicker: they say I have to have 3G for the GPS to work and the two times that the GPS has worked the best and stayed on for the longest amount of time (45 mins to a little over an hour without ever dropping out) was on the same stretch of road, on two different days, in a very remote area where I lose voice and data signal, completely. Perhaps the radio in the phone is the culprit?
I know this is long-winded, but I wanted to let everyone else know what I've tried and to hopefully arm you with some information to take to Apple and/or Verizon. I personally think they're about to have a bunch of angry customers over this. I've been severely irritated since I took delivery of mine on the eighth of Feb.