Just to clarify, this is not meant for general ptsn telephone calls correct?

Unless you get the other side onboard, and they have compatible hardware to decrypt the stream, i don't really see the utility of this, in regards to general ptsn calls.

Don't get me wrong, i think its a great idea, but only for special usage between two parties that have the capability/hardware/know how to set up an encrypted stream. And unless its a cross platform encryption system, it will only work with other n900's.

I'd just go with something like a vpn, and a sip gateway voip service. If you can find service providers for those services that won't bend over for the feds, then add some kind of encryption to the data stream, and your in business.

But once again, it has to be setup/compatible on both ends. If the other end of the call on the ptsn isn't encrypted, theres no vpn/service that prevents wiretapping of the unencrypted ptsn data.

No way around that, unless some kind of universal/cross platform/hardware ptsn encryption system is setup universally. But Uncle Sam wouldn't like that very much, and i don't see it happening anytime soon.