Can we turn on/off the GPS programmatically in iPhone?

A simple example:

//Init location manager 

CLLocationManager* locationManager = [ [ CLLocationManager alloc] init];
locationManager.delegate = self; //we must implement the protocol

//Choose your accuracy level

//To turn on gps (if it isn't on already)
[locationManager startUpdatingLocation];

//To turn gps off (if no other apps are listening)
[locationManager stopUpdatingLocation];

There is more than this, and you can monitor more or less accuracy, and even use wifi/ cell towers. Please read the example first for best usage.

Well the GPS will be turned on if you use the CLLocationManager.

The locationmanager will first start by getting the location via triangulation and then turn the GPS to get a more precise fix.

Previous to iOS 5 the behavior was not consistent for launch of phone setting from third party application, but in iOS5 this is improved.

If we are calling startUpdatingLoaction method as below code and if location service is off,the system alert will popup and if we tap setting button,it will navigate to phone setting.

CLLocationManager *locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
[locationManager startUpdatingLocation];