Po isn't thrilled about the trend of surveillance in this country and how easy it could be for them to listen in on cellphones. Leo says that the courts have held that metadata (where he is or who he's calling) isn't subject to a warrant. So the government can make a request for a "pen register," pay a fee and then they can know someone's exact whereabouts.
They can also obtain a warrant from a secret court called the Foreign Intelligence Surveillance Court (FISC). The NSA collects this data and keeps it for three years. The problem is, the NSA has capabilities far beyond what the law gives them. So Po is right to be concerned. But we asked for all of this after 9-11. Had we known just how pervasive they'd get, though, we may not have been so eager for the security.
End to end encryption is possible, where one party would encrypt the message and then send it to someone who has the key to decrypt it. This is the only way to have private conversations. It doesn't work for phone conversations, but it does exist for texting with an app called Secure Text. It also exists for email with PGP or SMIME. Leo recommends using OpenGPG at gpgtools.org. The problem with this is, both ends of the conversation has to understand it and use it for it to be effective.