I posted these same thoughts last time I saw a "secure" phone on slashdot. Apparently it was long enough ago that it's no longer in my post history?
Regardless, there are two options I am aware of: 1) end to end encryption or 2) insecure messages/communication
The problem with #1 is that it requires secure devices on BOTH ENDS of the communication. You get very little bonus security if your device is secure, but the text messages, emails, phone calles etc. go unencrypted over the wire. That's fine, but now I have to persuade my parents and all my friends to get THIS exact phone, understand how it works well enough to set it up, and actually use those features.
I have a lot of respect for Zimmerman, but I'm extremely skeptical.