A pay-as-you-go cellphone that is used to maintain privacy. Often used for illegal transactions, both parties use burner phones, which are trashed after a short while. There is often no registration required when purchasing the devices along with prepaid minutes, which makes tracing calls by law enforcement or a government agency nearly impossible.
Also for Other Privacy Issues
Although somewhat extreme, a few tech-savvy people use a burner phone to access apps that they need but fear might be stealing private information. In this case, the burner phone is a smartphone for only certain apps and does not have to be a pay-as-you-go phone. For example, people might use an iPhone all the time and occasionally an Android burner phone, or vice versa. The burner phone is never used to log onto financial websites that contain sensitive data.
The Burner App Option
A burner app may also be a solution. Using your existing phone, apps such as Burner, Hushed and Line2 provide an alternate phone number on a subscription basis. Google's VoIP service is another option (see Google Voice