You can use VPN Anyconnect or IPSec both (or 3rd party) will work for fully featured Jabber Client.
You may also have a look at Cisco Expressway. VPNless Firewalltraversal for Jabber Clients.
Expressway has already been released Jabber Clients supporting this feature are still beta. It supports IM&Presence, Softphone, Voicemail access, Directory via UDS. CTI Controll or Connect and Extend are not possible using expressway.