Cell data connection will let you acquire satellite faster by downloading the telemetry quickly, but has nothing to do with accuracy.

From what I hear the GPS antenna in phones are good at low latitude, but as you go north/south they run out of steam pretty fast.

I can't figure out why that would be the case. For directional satellite antennas, sure, you can only point them so low to the horizon, so if you're trying to aim at a geostationary satellite the further away from it's regular footprint you go, the worse it will work. But GPS doesn't work like that, the satellites are in medium earth orbit and cover the globe pretty evenly. GPS receiver antennas are typically either omnidirectional or are optimized for receiving signals from straight overhead.

As long as you aren't dependent on the terrestrial data network for maps, a cellphone GPS should work quite nicely anywhere on the globe. Now, with that said, I have no GPS experience outside of North America, so if there's something going on that I don't understand please let me know.

Just returned from extensive walking and navigating in a large city. I found that the latest and greatest Garmin had trouble acquiring and maintaining a signal in the urban canyons and that the iphone actually navigated better and more consistently. I bought a Mophie battery extender for my iphone as I was going through the battery so quickly. The advantage of this is that you do not have to turn off your phone or wait for it to charge up. You can use it in conjunction with your iphone battery. I did not get quite double the normal battery life of the iphone, but it was about 1 and 3/4 the normal life. It generally carried me through a full day, and I used the Garmin for those times outside the urban canyons.

In city the phones generally have advantage over GPS as they can use WPS when no satellite is available.

Be careful with that though, I've found that a non GPS signal is less than acurate. Maybe because I live in a good coverage area or have a phone with a good antanna or whatever but I hit a lot of towers right here which results in my non gps locaton having a lot of movement. I've turned off the aGPS and wifi location to keep it accurate.

You NEVER rely exclusively on technology for navigation, you have to be familiar with your routes and areas and stay oriented. I ALWAYS carry a hard copy map and maintain knowledge of my locations as I move. The technology can help in many ways, but it is an aid only. All that being said, I found the cell phone signal to be within about 150 feet of where I knew I was, while the GPS jumped around or lost signal. When trying to find a particular business or marking a waypoint, the technology is more helpful, and this was mostly impossible with the GPS.

On a side note, I would like to find the best iphone app which gives the functionality of a GPS (marking waypoints, distance to travel, navigating to a location). Any ideas out there let me know. Thanks.

I like iTopoMaps for this, not least of which because I can download quads and not be dependent on data connectivity. No affiliation.

Interesting. Which GPS receiver were you using? I have had no trouble maintaining lock with either my Garmin Nuvi or GPSMAP 60CSx. Both have the high-sensitivity receiver and the 60CSx has a very good antenna which helps.

I was using the 62st. I am more accustomed to the 60csx, and have had good luck with that as well. I was surprised at the difficulty the 62st had. But it was downtown San Francisco and some pretty tall buildings. it worked fine in areas of open sky like large intersections and lower buildings. I ended up using the two devices (which looked a bit strange to locals). I drove in with a Nuvi and had the same issues once I got into the downtown area. The signal would jump around at times or fix in a bad location a block away.

Interesting. I had a lock problem with one of the older receivers but haven't seen it with the Nuvi. I've heard others say the same regarding peeps preferring the 60 series over the 62. The 62 should have an even better receiver, but that doesn't seem to be the case.