A-GPS and GPS
Let's start by explaining what the A-GPS and how it differs from GPS. Most cell phones do not have enough good receivers who would be able to ensure reliable reception of signals in a room or between skyscrapers. It is here that comes to the assistance conditional so-called A-GPS, which in most other cell phones is simply called GPS. A-GPS (born Assisted GPS) system that speeds up the coordinates of a GPS-receiver the biggest problem for GPS receiver is the so-called "cold start". It was at this moment is search for satellites. Depending on external factors, the process may be delayed start, which not only causes discomfort, but also leads to increased energy consumption. A-GPS technology helps to cope not only with this problem, but few make life easier for GPS receiver.
With the iPhone, this means that the current position will be determined by GPS, Wi-Fi stations and mobile operators (artisans from Apple have managed to use all of this, only 2 antenna, which are located in unexpected places – a ring around the camera, audio-jack, metallic bezel around the screen, etc. All of these will handle data staging server. Therein lies the advantage of A-GPS to GPS: first is much faster, and the second "slow" during the "cold start" when looking for satellites. With a typical GPS receiver for positioning you need several strong signals and a certain amount of time to get the coordinates. With A-GPS support server itself tells your phone where the satellites of the near, the shortening the time to look. In addition, this approach saves more battery. Unlike many other phones, A-GPS in the iPhone will work without network connectivity, allowing you to use it in nature, and indeed anywhere in the world, where the satellite signal is caught (but do not forget that you will need Google Maps, it will load up in advance).
At the moment it is not known how fast the A-GPS will put the battery: iPhone will automatically turn itself on and off as needed positioning system that will keep the charge. Assumes that the active work of its (constant trekig position, etc.) it will consume all the same quite a lot. Realizing what a good after all GPS will be in the iPhone, we move on to the fun – to navigate. That's where Apple, as always in his repertoire. Current version of the SDK prohibits its use for navigation in real time (Real-Time Route Guidance). But it is not so bad, giant TomTom GPS industry announced that they are already working on a navigator for the iPhone. Apparently, large companies have to somehow get permission to use the SDK on an individual basis. Thus, we are waiting for additional spending to make the iPhone an acceptable use for navigation. But we, apparently, is no stranger :-).