If you want to allow the user to drop a pin for start and end, may I suggest that the user to be able to drag and zoom the map and holduse the 'hold' gesture to drop the pin. SetYou can set it by default with the first pin as the departure point and the 2nd pin as the destination point.
If your app allow userusers to keepkey in a Postal code and address of the location, you might want to have a separate screen for user to enter the 2 addresses. Allowing the application to set the current location (using the device GPS) will add value to your apps.
Simon