Prepaid phones and encrypted phones serve two different purposes. Encrypted phones protect the content of intercepted communications by scrambling (encrypting) the voice communications so that they can only be decrypted with a secret key. Prepaid phones sort of protect from targeted communications interception because if the attacker doesn't know the phone to target they may not be able to intercept communications from/to it (of course they may just intercept all communications, but then the problem is finding a needle in a haystack). Encrypted phones don't inherently protect you from traffic analysis, if an attacker determines your phone number they can see who you call and who calls you but they cannot determine what you say. Frequently switching prepaid phones does protect some from traffic analysis as the attacker will need to find your new number to continue being able to determine who is calling you and who you are calling. You can probably meet both goals by using an encrypted phone with frequently switched anonymously obtained SIMs though. Both of these systems for communications have flaws. Law enforcement agencies can identify when you switch your phone very quickly simply by monitoring the numbers that you are known to call and seeing when a new number calls these numbers. They can with high probability determine your new number in this way. The only way around this is for everyone you communicate with to frequently switch their numbers. Actually protecting from having your phone identified is quite hard to pull off if you try to accomplish it by switching the number frequently. Encrypted voice is certainly far better than nothing, but all kinds of fingerprinting attacks can gather information from encrypted voice streams. The CIA has been able to identify the language being spoken for some years now, even when the actual voice content is encrypted. There are also attacks that can pick out entire phrases and words through the encryption. This is because different languages / sentences create different interpacket timing characteristics that can be fingerprinted, and encryption doesn't hide the time delay between various packets of voice data. To protect from this sort of attack you will need to pad the voice data stream. My suggestion is to stick with encrypted text messages if you must use a phone. Better yet, use a smartphone that can use pidgin OTR and stick to using pidgin via Tor for your communications. This will protect the content of your communications as strong encryption is used on the text, and it will protect you from traffic analysis as the data is routed through Tor. If you absolutely need encrypted voice (hint: you do not), I would look into whispersys.