1. N900 has gps+agps it work regardless of if you are in coverage area or not, if you are out of cell range it takes longer to fix your position.
"The device has an autonomous GPS with optional A-GPS functionality" -- http://en.wikipedia.org/wiki/Nokia_N900

2. most phones and devices that use agps DO NOT have autonomous GPS, how it can kind of track you when you go out of cell range is by fixing on your last known good location then using data from the accelerometer and the compass. this works ok for about 1000 meters or untill you move off the current map display.

This is the case with my wifi iPad and ALL agps phones that I have ever tested.

"Although some AGPS receivers are capable of functioning as a GPS receiver, most are unable and would stop functioning once you go beyond the coverage area. GPS receivers are not restricted to the range of cellular sites and you can get a fix just about anywhere on the surface of the earth." -- http://www.differencebetween.net/tec...-gps-and-agps/

3 this site does not agree with your assessment that either the Samsung Galaxy S OR S2 have GPS + AGPS http://www.differencebetween.com/dif...d-vs-galaxy-s/