So many variations of explanation and confusion over here.

Ok so here's the idea. GPS 101.

iPhone uses hybrid positioning system that means GPS + aGPS. All of these are dictated by Location Services tab in the setting. Off this function and the ability to locate your position is gone.

1. GPS

GPS is the main method of positioning. The GPS receiver in the phone use the GPS satellites to relay all data and hence the location based on input from several satellites (terms as locked satellite), usually minimum of 3 satellites. The more satellites locked, the more accurate the position.

It's very accurate but it works great only at open space. The GPS signal is very poor indoors or in area with high towers or dense building populations. And it's also very slow especially if:

a) You have the cold start - meaning first time using the GPS unit.
b) You haven't use the GPS for a long time. (The GPS receiver in the phone only remember the last satellite position it was locked, so when the satellites move, it needs to search again)
c) You start the GPS at location A and close it. Then you start again the GPS at location B which is very far from location A. For the same reason in b), the GPS receiver needs to redo the search.

You can switch off all data services, 3G and even in flight mode, because it doesn't even needs any one of them. This method does not require a single cent.
2. aGPS

aGPS works great indoors but not very accurate. And it's very fast. That's why it's called aGPS, "a" here refers to "Assisted". GPS & aGPS work in harmony to complement each other weaknesses.

Problem is, there are so many types of aGPS. Some of them will incur data charges and some will not.

Some types of aGPS includes but not limited to:

a) Tower triangulation
b) Wifi-positioning
c) Network supplied GPS data

AFAIK, iPhone uses a) & b). In the case, iPhone can't detect a) it will uses b) and vice versa.

Tower triangulation doesn't requires data charges as well as Wifi-positioning. That's why your location can be detected even you have switch off both cellular data, 3G and data roaming.

However, type c) which download GPS orbital data requires data charges. But honestly, I do not know whether iPhone uses this method or not. This type obviously requires cellular data to be switch on.

So the question do aGPS incurs data charges? YES & NO. How do I know this? My Omnia uses method c) and everytime aGPS is used, my credit will be deducted.

Does aGPS for iPhone, incur data charges? I think it doesn't. most probably, because it uses GPS back up by a) & b).

Does this answer all doubts?

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Added on February 23, 2011, 12:03 pmRegarding the best navigation app for iPhone for the time being, my personal favorite is still PPG despite it's recent dissapointing update.

While I have never use TomTom, I have bought Sygic Mobile Maps 3D for SG&MY during the short $9.99 sale. Graphic is great, but room for improvement is abundance. Less hard on battery, and not as warm as PPG per se. No UI lag, a little bit of lagging during routing unlike PPG but as usual map database is nowhere near to PPG's MFM. Accuracy is absymal at some location as it gives my location on the adjacent taman street. POI details can't be taken right from the map, instead must go through the long menu list. But a quick glance on Sygic forum shows that many improvements are coming.

To those wondering the difference between Mobile Maps 3D MY&SG & Mobile Maps SEA, the SEA version obviously have larger map database for all other SEA countries but it's not 3D at city's location and no city guide. Thank God I've chosen the MM3D MY&SG because even though both will be upgraded to Aura, the SEA version has 3D and City guide as optional IAP which will cost 10 Euro each!

Btw, while Maction still hasn't improve on the UI lag etc of M8, I found out something interesting:



AR is coming to M8!

Those that can read Chinese perhaps can enlighten us what's the status of the program.

In case some of you can't figure out what is AR, it's Augmented Reality, which overlay application input on top of real-time video. That means, instead of the usual generated map, AR will project the route right in front of you! This technology has been used with some other GPS nav, it's nothing new. Plus other app looks more solid in terms of their AR routing. The bad news are:

1. You can't put the phone on your lap for example, it must be on the holder as the video needs to be on all the time. (This explains why they include video recording feature in M8!)

2. Sucking battery juice like monster, as this means video needs to be switch on all the way!

Wifi don't have A-GPS. Obviously it does not have GPS too. this is slightly misleading. A dedicated GPS device such as  Garmin DOES have GPS  without agps.

Maybe u can just say Ipad wifi does not have GPS CHIP inside?

You're right. Does not have A-GPS does not mean don't have GPS. What I meant it is obvious because Apple when launching
iPad did not say iPad WiFi have GPS. That's why since WiFi is not announced to have GPS, obviously it does not. I don't know
why people still asking if WiFi got. I mean, if I said WiFi version without mentioning it has 3G, obviously it does not have 3G.
I don't have to say its a WiFi version without 3G. 

Anyway, thanks for your comment. With your comment, I can explain it more clearly. LOL

"That's why since WiFi is not announced to have GPS, obviously it does not"

er doesnt make sense. what has wifi and 3g got to do with gps? How will we know if we have dont have GPS chip if apple doesnt say? why cant we assume there's wifi and gps chip inside too?

Your point only makes sense if apple announce there 2 version: wifi, wifi+3g+GPS

then it's obvious there's no gps in wifi version.

Yes. Recently went to a foreign country with my 16 3G ipad.

Before that i downloaded a full map apps for the town from the Appstore.

When arrive there i just open the map without even slotting a Sim Card or a wifi conn and it Navigates accurately through the map.

Yes. Recently went to a foreign country with my 16 3G ipad.

Before that i downloaded a full map apps for the town from the Appstore.

When arrive there i just open the map without even slotting a Sim Card or a wifi conn and it Navigates accurately through the map.

mean Ipad1 16GB 3G can support GPS too?