stream ciphers and realtime communications?

[Jonathan Rochkind <jrochkin@cs.oberlin.edu>]

Well, I finally did my duty and picked up a copy of Applied Cryptography. :)
I've only given it a cursory browing so far, but I have a question.
 
When I first saw reference to stream ciphers in the book, I imagined that they would be ideal for realtime encrypted communications, like voice (in cellular phones, perhaps).
But after reading further, it appears that stream ciphers aren't being used much
in this manner, or much at all.
Is this correct? I know that there are plenty of encryption protocols and methods for
realtime communications (clipper chip, for one), but do they just use block
ciphers with relatively small blocks? (Is the security of such things as RSA
and IDEA effected by size of block? There's got to be a minimum block that works;
you can't do IDEA on a single byte, or can you?)
 
Can anyone outline what kinds of methods are used for voice encryption and other realtime
methods, as contrasted with email and delayed transfer methods?