According to The Register, Cisco is currently adding encryption abilities into their phones and call manager software. The article’s kind of hard to follow–it claims that the 7960G currently has encryption support, which is news to me–but the general gist is that they’re planning on adding some sort of direct VPN support into most of their phones via software upgrades.
Knowing Cisco, the feature will be implemented in some odd manner (L2TP+1DES IPsec in the phone?) and will only work with the CallManager-specific SCCP image for the phones, not the SIP image.
On the other hand, if they actually added TLS/SSL support for SIP and SRTP, then that’d be a huge motivation for getting encryption in Asterisk.