Updating the Preferred Roaming List (PRL) on the user's device can resolve issues with cell signal and call drops, especially while traveling, as it provides the phone with updated information about which cell towers to connect to for the best service coverage. Resetting network settings would also refresh the device's connection with the network but does not specifically update the PRL. Updating the operating system does not directly affect the device's ability to connect to the best tower unless there is a specific bug related to mobile connectivity in the current version. Changing the device's location services modifies how the device uses GPS for location-based applications, which does not correlate directly with cellular network connectivity issues.