Asterisk via cell - Encrypted?

Hi. I have a client that is looking for an encrypted voip solution that uses a PDA-Phone of some sort to send the voice traffic over a Cellular broadband connection (EVDO, 3G, etc…).

Ideally, i’m looking for a PDA softphone that supports SRTP or ZRTP, but have had no luck so far in finding anything. An alternative solution would be to create a VPN between the cell phone and the VOIP server and then use something like SJPhone.

Has anyone done anything like this? I’d be interested in hearing your experiences.

There is a company working on it. I forgot their name. Google around. There were at the “Ettel” (I hope I am spelling it right) conference last year in San Fransisco.