Generally, it’s best to always be in contact with ATC for traffic advisories and immediate access to help. If you’re not communicating with anyone, most GPS systems can quickly provide frequencies for the nearest flight service station and ARTCC facility. And if you find yourself in dire need to communicate with someone and don’t have quick access to a frequency that will get you in touch with a controller, dial up 121.5. You should be familiar with this frequency as an emergency frequency. Don’t abuse it, but if you find yourself in a bind, by all means use it.