Voice encryption was available with the STU-III for a long long time.
When was the last time you saw a STU-III in an office? Ever? It's because the security capability isn't worth the trade off and friction it creates for business.
The dirty little secret is that the whole process of doing key exchange and verifying that you have a solid connection between two trusted parties is NOT a widely solved problem.
TRUST between two parties that have never met is NOT a solved problem at scale unless you consider SSL a solution and there are a lot of people who think that SSL is broken in many regards.
Think of all the features that a modern enterprise phone system has:
Call waiting
Three way calling
Conference bridges
Voicemail
CallerID
Call Parking
Assistant Mode
...et al.
Regulatory archiving
You don't get ANY of those with ANY commercially available secure phone system. The same problems you have with using secure email at scale you have with secure voice.
When was the last time you saw a STU-III in an office? Ever? It's because the security capability isn't worth the trade off and friction it creates for business.
The dirty little secret is that the whole process of doing key exchange and verifying that you have a solid connection between two trusted parties is NOT a widely solved problem.
TRUST between two parties that have never met is NOT a solved problem at scale unless you consider SSL a solution and there are a lot of people who think that SSL is broken in many regards.
Think of all the features that a modern enterprise phone system has:
Call waiting Three way calling Conference bridges Voicemail CallerID Call Parking Assistant Mode ...et al. Regulatory archiving
You don't get ANY of those with ANY commercially available secure phone system. The same problems you have with using secure email at scale you have with secure voice.