I am researching to find out how a iPhone/Anroid cell phone GPS works.
I've heard that some phones get GPS data from cell towers while other phones have a stand alone GPS receiver/system.
I'd appreciate some feedback and references.
All the "smart phones" have a GPS receiver. I suspect you are confused by E911 capability. This is the system to provide a location when you make a 911 call from a cell. Phones without GPS or with their GPS turned off will get an approximate location via cell site triangulation.